bpo-33083: Update "What's new" with math.factorial changes (GH-9109)

* Add elimination of non-int-like parameters in math.factorial to "What's new".

Doc/whatsnew/3.8.rst

@@ -272,6 +272,9 @@ Changes in the Python API
   success; an exception was raised on error under Unix.
   (Contributed by Berker Peksag in :issue:`2122`.)
 
+* The function :func:`math.factorial` no longer accepts arguments that are not
+  int-like. (Contributed by Pablo Galindo in :issue:`33083`.)
+
 
 CPython bytecode changes
 ------------------------