Turn on repository verification checksum feature

In 10.6 RCs, we shipped the repository checksum verification feature behind a feature flag to ensure GitLab.com was in a good state before we scheduled lots of these jobs.

I think we're in a good state now, so I think we should turn this on soon.

The flag is geo_repository_verification.

@dbalexandre @digitalmoksha Any reason we shouldn't start here?