Add What's New entry.

Author: avm19

doc/source/whatsnew/v2.3.0.rst

@@ -133,7 +133,7 @@ Interval
 Indexing
 ^^^^^^^^
 - Fixed bug in :meth:`Index.get_indexer` round-tripping through string dtype when ``infer_string`` is enabled (:issue:`55834`)
--
+- Bug in :class:`MaskedIndexEngine` affecting :meth:`Index.get_indexer` and downstream methods when ``NaN`` is located at or after position 128 (:issue:`58924`)
 
 Missing
 ^^^^^^^