Mirroring doesn't copy across all refs
### Summary
Mirroring doesn't copy across all refs
### Steps to reproduce
- Set up pull mirroring for a repository.
- Push a ref (that isn't a branch or tag) to the remote repository (e.g. refs/notes/signatures)
- Manually trigger a mirror pull
- Observe that the ref is not available from the mirror (e.g. `git fetch https://gitlab.com/hashbang/git-signatures refs/notes/signatures`)
### Example Project
https://gitlab.com/hashbang/git-signatures
### What is the current *bug* behavior?
ref is not present
### What is the expected *correct* behavior?
All references should be available from a mirror
issue