Fix gitlab:backup rake for hashed storage based repositories

What does this MR do?

Fix a regression introduced with the Hashed Storage repositories, that was not getting included in backups.

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

Why was this MR needed?

See: gitlab-org/gitlab-ce#39573

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 UX
  • Has been reviewed by Frontend
  • Has been reviewed by Backend
  • Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• Internationalization required/considered

What are the relevant issue numbers?

Closes #39573 (closed)