Resolve "Temporary repositories in Geo sync download are broken"

What does this MR do?

Constructs a new Repository object, instead of mutating a clone, when performing Geo sync to a temporary directory

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

Why was this MR needed?

This doesn't seem to fix any existing bugs in master, but I suspect this caused failures in 10.5, which were accidentally fixed in 10.6. I want to avoid a recurrence of the issue.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Review
  • Has been reviewed by Backend
• 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?

Closes #5485 (closed)