Isolate the fork network background migrations
What does this MR do?
Before the PopulateForkNetworksRange
spec would also call the
CreateForkNetworkMemberships
which we would count on in the spec.
With this, I'm isolating that, and counting only records created in this particular migration instead.
Why was this MR needed?
To avoid failures like the ones discussed in: https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/3392