[3.10] bpo-46104: Reduce use of pre-PEP 526 syntax in typing docs (GH-30148) (GH-30179)

Co-authored-by: Andrew Svetlov <andrew.svetlov@gmail.com>
(cherry picked from commit 6ada013df170b0afb6b61a0d942388c6fd81cbc9)


Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>