[3.12] gh-131417: Mention asyncio Future and Task in docs for generic classes list (GH-131422) (#131446)

gh-131417: Mention asyncio Future and Task in docs for generic classes list (GH-131422)

Mention asyncio Future and Task in docs for generic classes list
(cherry picked from commit 61b4b2c57c9327273f2e306bafa23cf2c70eac8e)

Co-authored-by: Andrew Svetlov <andrew.svetlov@gmail.com>