Added whatsnew entry

Author: BryanCutler

doc/source/whatsnew/v1.2.1.rst

@@ -29,6 +29,7 @@ Fixed regressions
 - Fixed regression in :meth:`read_csv` and other read functions were the encoding error policy (``errors``) did not default to ``"replace"`` when no encoding was specified (:issue:`38989`)
 - Fixed regression in :meth:`DataFrame.replace` raising ValueError when :class:`DataFrame` has dtype ``bytes`` (:issue:`38900`)
 - Fixed regression in :meth:`DataFrameGroupBy.diff` raising for ``int8`` and ``int16`` columns (:issue:`39050`)
+- Fixed regression in :meth:`DataFrame.groupby()` when aggregating an :class:`ExtensionDType` that could fail for non-numeric values (:issue:`38980`)
 
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