[3.9] bpo-41314: fixed annotations __future__ version (GH-21616) by miss-islington · Pull Request #21620 · python/cpython

PEP 563 was updated to change the release where `from __future__ import annotations` becomes the default (and only) behavior from 4.0 to 3.10. Update `__future__.py` and its docs to reflect this.
(cherry picked from commit 0028c14)

Co-authored-by: YoSTEALTH <35307184+YoSTEALTH@users.noreply.github.com>