DOC: Add whatsnew note

Author: Licht-T

doc/source/whatsnew/v0.23.0.txt

@@ -1246,6 +1246,7 @@ Indexing
 - Bug in ``Series.is_unique`` where extraneous output in stderr is shown if Series contains objects with ``__ne__`` defined (:issue:`20661`)
 - Bug in ``.loc`` assignment with a single-element list-like incorrectly assigns as a list (:issue:`19474`)
 - Bug in partial string indexing on a ``Series/DataFrame`` with a monotonic decreasing ``DatetimeIndex`` (:issue:`19362`)
+- Bug in ``.loc``, which cannot handle ``uint64`` input (:issue:`20722`)
 
 MultiIndex
 ^^^^^^^^^^