s_outdated_fixme frequently starts failing only after a PR is merged in. This leads to "cleanup" tickets that need to be scheduled and done later (e.g. WT-15922).

Rather than having the script only detect a closed ticket after the PR has been merged, we could extend it to fail if the current PR has references in the code.

Note that this is a little more subtle than it sounds. We can't simply fail on "in code review" tickets, since then another (unrelated) open PR could cause all PRs to fail. Rather, I suspect it's possible to pull the ticket number from Evergreen (via the PR title?) and test for that. But it's just an idea, there's probably something smarter we can do.