update whats new

Author: Hanspagh

doc/source/whatsnew/v1.1.3.rst

@@ -31,6 +31,7 @@ Bug fixes
 - Bug in :class:`Series` constructor where integer overflow would occur for sufficiently large scalar inputs when an index was provided (:issue:`36291`)
 - Bug in :meth:`DataFrame.stack` raising a ``ValueError`` when stacking :class:`MultiIndex` columns based on position when the levels had duplicate names (:issue:`36353`)
 - Bug in :meth:`isin()` when using NaN and a row length above 1,000,000 (:issue:`22205`)
+- Bug in :meth:`Series.isin` when using ``NaN`` and a row length above 1,000,000 (:issue:`22205`)
 
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