[3.13] GH-122482: Make About IDLE direct discussion to DPO (GH-122483) (#122485)

Currently, idle-dev@python.org and idle-dev mailing list
serve to collect spam (90+%).  Change About IDLE to direct
discussions to discuss.python.org.  Users are already
doing so.
(cherry picked from commit 29c04dfa2718dd25ad8b381a1027045b312f9739)

Co-authored-by: Terry Jan Reedy <tjreedy@udel.edu>