[3.10] gh-93453: Only emit deprecation warning in asyncio.get_event_loop when a new event loop is created (#100059)

It no longer emits a deprecation warning if the current event loop was set.

(cherry picked from commit 3fae04b10e2655a20a3aadb5e0d63e87206d0c67)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
Co-authored-by: Łukasz Langa <lukasz@langa.pl>

• Doc/library/asyncio-eventloop.rst[diff]
• Doc/library/asyncio-llapi-index.rst[diff]
• Doc/library/asyncio-policy.rst[diff]
• Lib/asyncio/events.py[diff]
• Lib/test/test_asyncio/test_base_events.py[diff]
• Lib/test/test_asyncio/test_events.py[diff]
• Lib/test/test_asyncio/test_futures.py[diff]
• Lib/test/test_asyncio/test_streams.py[diff]
• Lib/test/test_asyncio/test_tasks.py[diff]
• Lib/test/test_asyncio/test_unix_events.py[diff]
• Lib/test/test_coroutines.py[diff]
• Misc/NEWS.d/next/Library/2022-12-02-13-05-00.gh-issue-93453.EFj1NN.rst[Added - diff]
• Modules/_asynciomodule.c[diff]