bpo-46604: fix function name in ssl module docstring (GH-31064)

The function fetch_server_certificate is replaced by get_server_certificate in the module. I reflected the change in the module docstrings.

Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>
(cherry picked from commit feca9bbd1f6489f2b6d2783bfc22fdb96e45b69f)

Co-authored-by: Kossi GLOKPOR <83467320+glk0@users.noreply.github.com>