pythongh-104992: [What's New in 3.11] Document unittest.TestProgram.usageExit's deprecation (pythonGH-104994)

Document unittest.TestProgram.usageExit's pending removal in 3.13
(cherry picked from commit 7df861c)

Co-authored-by: Hugo van Kemenade <hugovk@users.noreply.github.com>

Author: hugovk

Doc/whatsnew/3.11.rst

@@ -1858,6 +1858,10 @@ Standard Library
 
   (Contributed by Erlend E. Aasland in :issue:`5846`.)
 
+* :meth:`~!unittest.TestProgram.usageExit` is marked deprecated, to be removed
+  in 3.13.
+  (Contributed by Carlos Damázio in :gh:`67048`.)
+
 
 .. _whatsnew311-pending-removal:
 .. _whatsnew311-python-api-pending-removal: