Today after Mergify opened a Backport PR, it will stay open until someone manually close the backport PR , also we can't track using labels which backport was done or not since there is no indication for that except digging into the PR and looking for a comment or a commit ref
The following changes were made in this PR:
* trigger add-label-when-promoted.yaml also when the push was made to `branch-x.y`
* Replace label `backport/x.y` with `backport/x.y-done` in the original PR (this will automatically update the original Issue as well)
* Add a comment on the backport PR and close it
Fixes: https://github.com/scylladb/scylladb/issues/19441Closesscylladb/scylladb#19442
394cba3e4b