* ci: run required checks on merge-queue groups
Add the merge_group trigger to CI and PR title validation so every required
check reports on the queued group's exact head. Group runs use exact-head
concurrency groups that pushes cannot cancel, classify the group's combined
diff from its base (a non-ancestor base fails planning), and keep the CI
required gate running when a group is cancelled so it fails instead of
reporting a skipped check. Title validation checks every squash commit
subject between the group base and head.
* ci: read the merge-group comparison from a file
morluto
5efaedda88