Backport PR #56312 on branch 2.2.x (DOC: Add whatsnew for concat regression) (#56686)

Backport PR #56312: DOC: Add whatsnew for concat regression

Co-authored-by: Thomas Li <[email protected]>

Author: meeseeksmachine

doc/source/whatsnew/v2.2.0.rst

@@ -761,6 +761,7 @@ Datetimelike
 - Bug in parsing datetime strings with nanosecond resolution with non-ISO8601 formats incorrectly truncating sub-microsecond components (:issue:`56051`)
 - Bug in parsing datetime strings with sub-second resolution and trailing zeros incorrectly inferring second or millisecond resolution (:issue:`55737`)
 - Bug in the results of :func:`to_datetime` with an floating-dtype argument with ``unit`` not matching the pointwise results of :class:`Timestamp` (:issue:`56037`)
+- Fixed regression where :func:`concat` would raise an error when concatenating ``datetime64`` columns with differing resolutions (:issue:`53641`)
 
 Timedelta
 ^^^^^^^^^