[core] Fix support for upcoming Python 3.12 (#8130)

This also adds the following test runners:
- `3.12-dev` on `ubuntu-latest`
- `3.12-dev` on `windows-latest`
- `pypy-3.10` on `ubuntu-latest`

Authored by: Grub4K

yt_dlp/extractor/motherless.py

@@ -151,7 +151,7 @@ class MotherlessIE(InfoExtractor):
                     'd': 'days',
                 }
                 kwargs = {_AGO_UNITS.get(uploaded_ago[-1]): delta}
-                upload_date = (datetime.datetime.utcnow() - datetime.timedelta(**kwargs)).strftime('%Y%m%d')
+                upload_date = (datetime.datetime.now(datetime.timezone.utc) - datetime.timedelta(**kwargs)).strftime('%Y%m%d')
 
         comment_count = len(re.findall(r'''class\s*=\s*['"]media-comment-contents\b''', webpage))
         uploader_id = self._html_search_regex(