Report ref not found to agent
We allow to specify ref (since !799 (merged)) for gitops and config repos. Sometimes users make mistakes but we don't return an error to them, just send it to Sentry. This MR makes it so that kas returns an error instead of sending to Sentry.
Errors look like this:
GitOps: repository poll failed: FileNotFound: InfoRefsUploadPack: file/directory/ref not found: refs/heads/production
and
Config: repository poll failed: FileNotFound: InfoRefsUploadPack: file/directory/ref not found: develop