Don't update PRs that are already enqueued in the Merge Queue #41903
Description
Describe the proposed change(s).
Something we've discussed before, but don't seem to have an Issue for - when a PR is in the Merge Queue, Renovate shouldn't update that branch as it can lead to the commit message being out-of-date with the changes that actually got merged
(Either part of this or a separate one: we should also detect this for GitLab's Merge Trains)
(Surprising behaviour - I would expect the title for the commit being fixed on time-of-enqueue)