[3.14] Fix typing.TYPE_CHECKING docs to reflect PEP 649. (GH-134813) (#134822)

Fix typing.TYPE_CHECKING docs to reflect PEP 649. (GH-134813)

typing.TYPE_CHECKING should no longer steer users towards
manual or automatic stringization (and PEP 563); PEP 649
makes all that unnecessary.
(cherry picked from commit d7256ae4d781932b3b43b162e8425abdb134afa6)

Co-authored-by: larryhastings <larry@hastings.org>