Resolve "TestEnv#set_repo_refs fails to update refs sometimes"

What does this MR do?

This merge request solves an error that would happen in development when a new branch/commit/ref was added to gitlab-test but the bare repos under tmp/tests/gitlab-test_bare/tmp/tests/gitlab-test-fork_bare wouldn't get updated when git fetch was run.

The bare repos are removed the first time TestEnv#set_repo_refs fails, so that newly cloned bare repos have the correct refs.

Are there points in the code the reviewer needs to double check?

The branch will be profiled in Redash, in any case.

Why was this MR needed?

Because it was annoying to ask people to rm -rf tmp/tests a few times per day! :)

What are the relevant issue numbers?

Closes #31562 (closed)