Add merge queue trigger for required jobs

I have "Plan" as a required check in my CICD, and merge queues require this to get triggered even if it's just skipped over. Therefore I added the line `merge_group: # Trigger in the merge queue, but skip the job` after the `cargo dist init` generation.

I've had to do this for other projects, where I need a required check to "skip" in the merge queue, otherwise the merge queue will be left hanging waiting for a status.