[3.13] gh-109975: Suggest ``pynntp`` instead of ``nntplib`` (GH-124830) (#124966)

gh-109975: Suggest ``pynntp`` instead of ``nntplib`` (GH-124830)

The ``nntplib`` library has been deleted from PyPI by its author.
(cherry picked from commit ac9648243dc0f5cb34c93621e507a98cf90550ea)

Co-authored-by: Christian Clauss <cclauss@me.com>