[3.13] 3.13 What's New: Add PEP 702 (GH-118922) (#119062)

I honestly forgot this slipped into 3.13, but I think it's worth highlighting more, as it is a PEP-sized change that makes the type system significantly more powerful.

@Yhg1s I think it's also worth mentioning in your release announcements.
(cherry picked from commit ee13797dec988884f8792144fe5b3d7f5c8083c9)

Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>