Geo: Gitlab::Git::CommandError (13:exit status 128) when calculating checksums

https://sentry.gitlap.com/gitlab/gitlabcom/issues/179781/

I suspect this happens because when Gitaly can't find the repository on disk, but it would be good to verify.

Fixes:

1. Ruby - https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/5486
2. Gitaly - gitaly!697 (merged)

/cc: @dbalexandre