Allow the git circuit breaker to correctly handle missing repository storages

What does this MR do?

Fixes a NoMethodError in production by introducing a null object for circuit breakers

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
• 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

What are the relevant issue numbers?

Closes #36549 (closed)