[3.12] gh-120345: Fix incorrect use of the :class: role with the "()" suffix (GH-120347) (GH-120412)

* Remove "()" when refer to a class as a type.
* Use :func: when refer to a callable.
* Fix reference to the datetime.astimezone() method.
(cherry picked from commit 92c9c6ae147e1e658bbc8d454f8c7b2c4dea31d1)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>