Skip repository-changing events on Geo secondaries if the repository hasn't been backfilled yet
Per https://gitlab.com/gitlab-org/gitlab-ee/issues/4869
If a legacy-storage project that hasn't yet been backfilled on the secondary is renamed, we try (and fail) to move the project and wiki repositories. However, we know this will fail (and is unnecessary) - we can check the project registry and see that it's not been synced yet.
I think we should have this awareness in all Geo event-handling code, to make it more resilient in the backfill phase - there's a lot going on at this time, and the more intelligent we can be about reporting errors, the better.