Avoid creating superfluous namespaces on Geo secondaries during sync

What does this MR do?

When redownloading a repository, Geo creates a superfluous namespace.

At present, given a project root/test-snapshot, a successful redownload gives this result:

repositories/
  root/
    test-snapshot/
    test-snapshot.git/

The test-snapshot directory is empty, but shouldn't be present.

We also have repositories/@failed-geo-sync/root/test-snapshot. I've not looked in any detail into what changes here, but again, it's not sensible to create the full directory before trying to mv the repository over.

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

Why was this MR needed?

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Review
  • Has been reviewed by Backend
• EE specific content should be in the top level /ee folder
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• Internationalization required/considered
• If paid feature, have we considered GitLab.com plan and how it works for groups and is there a design for promoting it to users who aren't on the correct plan
• End-to-end tests pass (package-qa manual pipeline job)

What are the relevant issue numbers?