[3.15] gh-151942: Fix all Sphinx nitpicks in the 2.5 What's New (GH-153120) (#153499)

(cherry picked from commit fb00514)

Co-authored-by: Stan Ulbrych <stan@python.org>

Author: miss-islington

Doc/tools/.nitignore

@@ -34,5 +34,4 @@ Doc/library/xml.sax.rst
 Doc/library/xmlrpc.client.rst
 Doc/library/xmlrpc.server.rst
 Doc/whatsnew/2.4.rst
-Doc/whatsnew/2.5.rst
 Doc/whatsnew/2.6.rst