bpo-45449: add note about PEP 585 in collections.abc's documentation (GH-29047) (GH-29067)

Signed-off-by: Filipe Laíns <lains@riseup.net>

Co-authored-by: Łukasz Langa <lukasz@langa.pl>
(cherry picked from commit 7bafa0cf586227987d3d662264d491e3780024b7)
2 files changed