Geo secondary proxying: git SSH operations fail when project not accessible on secondary

As found in &6418 (comment 707928780), if the project is not accessible on the secondary, git SSH operations fail with:

rpc error: code = NotFound desc = GetRepoPath: not a git repository: "/var/opt/gitlab/git-data/repositories/@hashed/ef/2d/ef2d127de37b942baad06145e54b0c619a1f22327b2ebbcfbec78f5564afe39d.git"

We should look into always proxying this to the primary if the repo doesn't exist, similar to what happens for HTTP(s) operations?