Background: To make sure we've backported everything correctly and that there's nothing else wrong, let's set up the wiki at https://thegoodplace.wmflabs.org/ to use the REL1_35 branch. This will mean also switching all extensions and skins to REL1_35 as well (where applicable; some have master compatibility).
Watchlist expiry will not be stable for 1.35.0, so the testing effort here is solely to make sure nothing broke with the feature flag turned off. Focus should be around watchlist-related things and notifications.
Testing can also be done at the temporary wiki created at https://patchdemo.wmflabs.org/wikis/96b1dbfd1c76008c2f5aa2ce8633e9de/w/index.php/Main_Page
- Test things that our watchlist expiry work might have broken for MediaWiki 1.35
- Provide an assessment of findings (i.e., Did you encounter any issues? If so, what were the issues and how can we potentially fix them?).