Geo - The count to find the numbers of repository|wikis that verification failed are wrong

Summary

The number of verification failures is the same as the number of mismatches because when having a mismatch we set the repository_checksum_mismatch column to true, and store an error message in the last_repository_verification_failure column as well.

See https://dashboards.gitlab.net/d/YoKVGxSmk/gcp-failover-gcp?orgId=1

Possible fixes

We have two options:

1. Check if the repository_checksum_mismatch is false both on Geo::ProjectRegistry.verification_failed_repos, and ~Geo::ProjectRegistry.verification_failed_wikis scopes.
2. Does not store an error message in the last_repository_verification_failure column when checksum mismatch.

/cc @stanhu @toon @digitalmoksha