This reverts commit d54e6cd6.

https://gitlab.com/gitlab-org/gitlab/-/merge_requests/98152 removed
SeedHelper and the associated gitlab-git-test. However, it appears
that Workhorse has a symlink for this repository for its own tests
(https://gitlab.com/gitlab-org/gitlab/-/merge_requests/96553).

Relates to https://gitlab.com/gitlab-org/omnibus-gitlab/-/issues/7221