Move to explicitly creating a new loop (#3164)

* Move to explicitly creating a new loop

- >= 3.10 add a warning that `get_event_loop` will not automatically create a loop
- Move to explicit API

Test:
- `python3.11 -m venv --upgrade-deps /tmp/tb`
  - `/tmp/tb/bin/pip install -e .`
  - Install deps and no blackd as aiohttp + yarl can't build still with 3.11
  - https://github.com/aio-libs/aiohttp/issues/6600
- `export PYTHONWARNINGS=error`
```
cooper@l33t:~/repos/black$ /tmp/tb/bin/black .
All done! ✨ 🍰 ✨


44 files left unchanged.
```

Fixes #3110

* Add to CHANGES.md

* Fix a cooper typo yet again

* Set default asyncio loop to our explicitly created one + unset on exit

* Update CHANGES.md

Fix my silly typo.

Co-authored-by: Thomas Grainger <tagrain@gmail.com>

Co-authored-by: Cooper Ry Lees <me@wcooperlees.com>
Co-authored-by: Thomas Grainger <tagrain@gmail.com>