Fix validation error type `GL03` and check in CI

[MarckK]

Problem description

In order to have a continuous check by the CI on validation error GL03 (Double line break found; please use only one blank line to separate sections or paragraphs, and do not leave blank lines at the end of docstrings), fixing them in the code base enables the addition to the CI for automated testing in the future.

GL03 has 99 occurrences (see overview of the errors), including:

method	file	file_line	github_lin
pandas.Timedelta	None	NaN	https://github.com/pandas-dev/pandas/blob/master/None#LNone
pandas.Timedelta.max	None	NaN	https://github.com/pandas-dev/pandas/blob/master/None#LNone
pandas.Timedelta.min	None	NaN	https://github.com/pandas-dev/pandas/blob/master/None#LNone
pandas.SparseArray	pandas/core/arrays/sparse.py	505.0	https://github.com/pandas-dev/pandas/blob/master/pandas/core/arrays/sparse.py#L505
pandas.DataFrame.agg	pandas/core/frame.py	6291.0	https://github.com/pandas-dev/pandas/blob/master/pandas/core/frame.py#L6291
pandas.DataFrame.aggregate	pandas/core/frame.py	6291.0	https://github.com/pandas-dev/pandas/blob/master/pandas/core/frame.py#L6291
pandas.DataFrame.compound	pandas/core/generic.py	10038.0	https://github.com/pandas-dev/pandas/blob/master/pandas/core/generic.py#L10038
pandas.DataFrame.cummax	pandas/core/generic.py	10986.0	https://github.com/pandas-dev/pandas/blob/master/pandas/core/generic.py#L10986
pandas.DataFrame.cummin	pandas/core/generic.py	10986.0	https://github.com/pandas-dev/pandas/blob/master/pandas/core/generic.py#L10986
pandas.DataFrame.cumprod	pandas/core/generic.py	10986.0	https://github.com/pandas-dev/pandas/blob/master/pandas/core/generic.py#L10986
pandas.DataFrame.cumsum	pandas/core/generic.py	10986.0	https://github.com/pandas-dev/pandas/blob/master/pandas/core/generic.py#L10986
pandas.DataFrame.kurt	pandas/core/generic.py	10941.0	https://github.com/pandas-dev/pandas/blob/master/pandas/core/generic.py#L10941
pandas.DataFrame.kurtosis	pandas/core/generic.py	10941.0	https://github.com/pandas-dev/pandas/blob/master/pandas/core/generic.py#L10941
pandas.DataFrame.mad	pandas/core/generic.py	9997.0	https://github.com/pandas-dev/pandas/blob/master/pandas/core/generic.py#L9997
pandas.DataFrame.mean	pandas/core/generic.py	10941.0	https://github.com/pandas-dev/pandas/blob/master/pandas/core/generic.py#L10941
pandas.DataFrame.median	pandas/core/generic.py	10941.0	https://github.com/pandas-dev/pandas/blob/master/pandas/core/generic.py#L10941
pandas.DataFrame.skew	pandas/core/generic.py	10941.0	https://github.com/pandas-dev/pandas/blob/master/pandas/core/generic.py#L10941
pandas.DataFrame.to_html	pandas/core/frame.py	2206.0	https://github.com/pandas-dev/pandas/blob/master/pandas/core/frame.py#L2206
pandas.melt	pandas/core/reshape/melt.py	21.0	https://github.com/pandas-dev/pandas/blob/master/pandas/core/reshape/melt.py#L21
pandas.describe_option	None	NaN	https://github.com/pandas-dev/pandas/blob/master/None#LNone
pandas.reset_option	None	NaN	https://github.com/pandas-dev/pandas/blob/master/None#LNone
pandas.get_option	None	NaN	https://github.com/pandas-dev/pandas/blob/master/None#LNone
pandas.set_option	None	NaN	https://github.com/pandas-dev/pandas/blob/master/None#LNone
pandas.core.groupby.GroupBy.head	pandas/core/groupby/groupby.py	2039.0	https://github.com/pandas-dev/pandas/blob/master/pandas/core/groupby/groupby.py#L2039
pandas.core.groupby.GroupBy.mean	pandas/core/groupby/groupby.py	1082.0	https://github.com/pandas-dev/pandas/blob/master/pandas/core/groupby/groupby.py#L1082
pandas.core.groupby.GroupBy.nth	pandas/core/groupby/groupby.py	1530.0	https://github.com/pandas-dev/pandas/blob/master/pandas/core/groupby/groupby.py#L1530
pandas.core.groupby.GroupBy.tail	pandas/core/groupby/groupby.py	2067.0	https://github.com/pandas-dev/pandas/blob/master/pandas/core/groupby/groupby.py#L2067
pandas.core.groupby.DataFrameGroupBy.corr	None	NaN	https://github.com/pandas-dev/pandas/blob/master/None#LNone
pandas.core.groupby.DataFrameGroupBy.cov	None	NaN	https://github.com/pandas-dev/pandas/blob/master/None#LNone
pandas.core.groupby.DataFrameGroupBy.diff	None	NaN	https://github.com/pandas-dev/pandas/blob/master/None#LNone
...	...	...	...
pandas.Series.to_numpy	pandas/core/base.py	866.0	https://github.com/pandas-dev/pandas/blob/master/pandas/core/base.py#L866
pandas.Series.agg	pandas/core/series.py	3427.0	https://github.com/pandas-dev/pandas/blob/master/pandas/core/series.py#L3427
pandas.Series.aggregate	pandas/core/series.py	3427.0	https://github.com/pandas-dev/pandas/blob/master/pandas/core/series.py#L3427
pandas.Series.cummax	pandas/core/generic.py	10986.0	https://github.com/pandas-dev/pandas/blob/master/pandas/core/generic.py#L10986
pandas.Series.cummin	pandas/core/generic.py	10986.0	https://github.com/pandas-dev/pandas/blob/master/pandas/core/generic.py#L10986
pandas.Series.cumprod	pandas/core/generic.py	10986.0	https://github.com/pandas-dev/pandas/blob/master/pandas/core/generic.py#L10986
pandas.Series.cumsum	pandas/core/generic.py	10986.0	https://github.com/pandas-dev/pandas/blob/master/pandas/core/generic.py#L10986
pandas.Series.kurt	pandas/core/generic.py	10941.0	https://github.com/pandas-dev/pandas/blob/master/pandas/core/generic.py#L10941
pandas.Series.mad	pandas/core/generic.py	9997.0	https://github.com/pandas-dev/pandas/blob/master/pandas/core/generic.py#L9997
pandas.Series.mean	pandas/core/generic.py	10941.0	https://github.com/pandas-dev/pandas/blob/master/pandas/core/generic.py#L10941
pandas.Series.median	pandas/core/generic.py	10941.0	https://github.com/pandas-dev/pandas/blob/master/pandas/core/generic.py#L10941
pandas.Series.skew	pandas/core/generic.py	10941.0	https://github.com/pandas-dev/pandas/blob/master/pandas/core/generic.py#L10941
pandas.Series.kurtosis	pandas/core/generic.py	10941.0	https://github.com/pandas-dev/pandas/blob/master/pandas/core/generic.py#L10941
pandas.Series.compound	pandas/core/generic.py	10038.0	https://github.com/pandas-dev/pandas/blob/master/pandas/core/generic.py#L10038
pandas.Series.dt.dayofweek	pandas/core/accessor.py	80.0	https://github.com/pandas-dev/pandas/blob/master/pandas/core/accessor.py#L80
pandas.Series.dt.weekday	pandas/core/accessor.py	80.0	https://github.com/pandas-dev/pandas/blob/master/pandas/core/accessor.py#L80
pandas.Series.dt.is_month_start	pandas/core/accessor.py	80.0	https://github.com/pandas-dev/pandas/blob/master/pandas/core/accessor.py#L80
pandas.Series.dt.is_month_end	pandas/core/accessor.py	80.0	https://github.com/pandas-dev/pandas/blob/master/pandas/core/accessor.py#L80
pandas.Series.dt.is_quarter_start	pandas/core/accessor.py	80.0	https://github.com/pandas-dev/pandas/blob/master/pandas/core/accessor.py#L80
pandas.Series.dt.is_quarter_end	pandas/core/accessor.py	80.0	https://github.com/pandas-dev/pandas/blob/master/pandas/core/accessor.py#L80
pandas.Series.dt.is_year_start	pandas/core/accessor.py	80.0	https://github.com/pandas-dev/pandas/blob/master/pandas/core/accessor.py#L80
pandas.Series.dt.is_year_end	pandas/core/accessor.py	80.0	https://github.com/pandas-dev/pandas/blob/master/pandas/core/accessor.py#L80
pandas.Series.dt.is_leap_year	pandas/core/accessor.py	80.0	https://github.com/pandas-dev/pandas/blob/master/pandas/core/accessor.py#L80
pandas.core.window.Rolling.aggregate	pandas/core/window.py	1678.0	https://github.com/pandas-dev/pandas/blob/master/pandas/core/window.py#L1678
pandas.core.window.Expanding.aggregate	pandas/core/window.py	1956.0	https://github.com/pandas-dev/pandas/blob/master/pandas/core/window.py#L1956
pandas.Series.ptp	pandas/core/generic.py	10941.0	https://github.com/pandas-dev/pandas/blob/master/pandas/core/generic.py#L10941
pandas.Panel.compound	pandas/core/generic.py	10038.0	https://github.com/pandas-dev/pandas/blob/master/pandas/core/generic.py#L10038
pandas.Panel.kurt	pandas/core/generic.py	10941.0	https://github.com/pandas-dev/pandas/blob/master/pandas/core/generic.py#L10941
pandas.Panel.kurtosis	pandas/core/generic.py	10941.0	https://github.com/pandas-dev/pandas/blob/master/pandas/core/generic.py#L10941
pandas.Panel.mad	pandas/core/generic.py	9997.0	https://github.com/pandas-dev/pandas/blob/master/pandas/core/generic.py#L9997

Todo:

• get rid of the errors in the code base
• update the code_check.sh script to take into account the GL03 type of errors