PEP 646: Mark Final - Githubissues

[X] Final implementation has been merged (including tests and docs)
[X] PEP matches the final implementation
[X] Any substantial changes since the accepted version approved by the SC/PEP delegate
[X] Pull request title in appropriate format (PEP 123: Mark Final)
[X] Status changed to Final (and Python-Version is correct)
[X] Canonical docs/spec linked with a canonical-doc directive (or canonical-pypa-spec for packaging PEPs, or canonical-typing-spec for typing PEPs)

Fixes python/cpython#115528.

python / peps