Update deprecated call to frame.append in quidel_covidtest #1518
Description
The Quidel indicator generates the following warning message:
covidcast-indicators/quidel_covidtest/delphi_quidel_covidtest/pull.py:65: FutureWarning: The frame.append method is deprecated and will be removed from pandas in a future version. Use pandas.concat instead.
We should update pull.py to use concat.
Not urgent, just needs to happen before pandas removes support for frame.append entirely.