Added whatsnew entry

Author: BryanCutler

doc/source/whatsnew/v1.2.0.rst

@@ -729,6 +729,7 @@ I/O
 - :meth:`read_fwf` was inferring compression with ``compression=None`` which was not consistent with the other :meth:``read_*`` functions (:issue:`37909`)
 - :meth:`DataFrame.to_html` was ignoring ``formatters`` argument for ``ExtensionDtype`` columns (:issue:`36525`)
 - Bumped minimum xarray version to 0.12.3 to avoid reference to the removed ``Panel`` class (:issue:`27101`)
+- Bug in :class:`Datetime64Formatter` that caused error on string representation with extension types of datetime64 values and ndim > 1 (:issue:`38390`)
 
 Period
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