One of our developers checked in (and pushed) a secure file.
I removed the file from their history, and did a push --force, in order to get the new history out there, which now doesn't include the file.
However, the orphaned check-in from before is still referenced in the project "Activity", and if I click on the hash then I can still see it that checkin, and the file.
Because it's no longer referenced by the master/head, I assume this orphan checkin will vanish the next time that GitLab carries out a garbage collection. But I'd like that to happen now, so that the secure file is no longer accessible.
How can I force this to happen?