Adopt Github merge queues

We would like to enable the new merge queue feature to avoid near-simultaneous commits having to update and re-run tests: https://github.blog/changelog/2023-02-08-pull-request-merge-queue-public-beta/

We tried it and PR #5868 got stuck, we think because of this: https://github.com/orgs/community/discussions/46757 "make sure your Action workflow(s) are properly configured to trigger on merge_group event"

So that's one action item.

The other is that right now with merge queues there is no option to modify the commit message on merge. They may add that later. But, it looks like we can now set it to use the PR title+desc -- maybe that is better in general as that can be reviewed prior to the squash: https://github.blog/changelog/2022-08-23-new-options-for-controlling-the-default-commit-message-when-merging-a-pull-request/