[Geo] Don't mark sync as successful if repo does not exist because of some problems

What does this MR do?

A secondary node marks every sync as successful if the repository does not exist. While it's OK for the majority of the cases it does not take into account some possible problems with NFS servers availability.

To make more precise decisions we could make use of repository checksum. If one exists but the repo doesn't, it's an indicator that something is wrong with the infrastructure.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Performance and testing

• Tests added for this feature/bug
• Tested in all supported browsers
• End to end tests added if this MR has ~"Requires e2e tests" label

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Closes #5067 (closed)