Forked repositories not having objects deduped and using excessive disk after forking

We have noticed new forked repositories are taking up the full amount of space as their parent repository instead of having their Git objects deduped. I believe this began after upgrading to 15.7.

I suspect this is the same root cause as gitlab!108970 (merged). And I'm guessing https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/workers/object_pool/join_worker.rb#L22 might be where the change is needed.