fix issue number on bug addition in whatsnew doc

Author: KevsterAmp

doc/source/whatsnew/v3.0.0.rst

@@ -539,7 +539,7 @@ Conversion
 - Bug in :meth:`DataFrame.update` bool dtype being converted to object (:issue:`55509`)
 - Bug in :meth:`Series.astype` might modify read-only array inplace when casting to a string dtype (:issue:`57212`)
 - Bug in :meth:`Series.reindex` not maintaining ``float32`` type when a ``reindex`` introduces a missing value (:issue:`45857`)
-- Bug in :meth:`Series.isna` returning ``bool`` instead of ``bool[pyarrow]`` for Arrow-based Series (:issue:`59431`)
+- Bug in :meth:`Series.isna` returning ``bool`` instead of ``bool[pyarrow]`` for Arrow-based Series (:issue:`59436`)
 
 Strings
 ^^^^^^^