Added whatsnew entry

Author: BryanCutler

Diff for: doc/source/whatsnew/v1.2.1.rst

@@ -24,6 +24,7 @@ Fixed regressions
 - Fixed regression in :func:`read_excel` with non-rawbyte file handles (:issue:`38788`)
 - Bug in :meth:`read_csv` with ``float_precision="high"`` caused segfault or wrong parsing of long exponent strings. This resulted in a regression in some cases as the default for ``float_precision`` was changed in pandas 1.2.0 (:issue:`38753`)
 - Fixed regression in :meth:`Rolling.skew` and :meth:`Rolling.kurt` modifying the object inplace (:issue:`38908`)
+- Fixed regression in :meth:`DataFrame.groupby()` when aggregating an :class:`ExtensionDType` that could fail for non-numeric values (:issue:`38980`)
 
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