Optionally, don't assign tickets where CI fails

For Arti, we'd like the option to not automatically assign review on tickets where CI is failing. I'm not sure if we'd want to turn it on or not; sometimes CI is broken on main for a day here and there.

Conceivably this tool should write a message on the ticket when it decides not to assign it, so that things don't get confusing. But that might lead to a more general "helpful message bot"; not that that would be a bad thing.

It might also be a good idea to have this rule apply to some users and not others: I'm unsure about declining to assign reviewers to less experienced volunteers, since sometimes they need communication to understand what CI is telling them.

@trinity-1686a asked to get an @ on this ticket.