PR action to require/encourage some things on a PR

[cassidyjames]

Could require:

• Class: Changes title format. Wouldn't need to be too clever, just look for a word/phrase and colon at the beginning probably
• A change to an AppData file. Would need an opt-out when there are no user-facing changes, maybe.
• No changes to po files (since that's managed by Weblate)
• Updated screenshot? Would need an opt-out when there are no user-facing changes.
• …anything else?

The idea is to help us not miss common style/process things.