Ensure CI runner has access to private registry.
This ensures the CI runner has access to the registry in the build step.
The registry provides nightly database backups, but requires auth to access. The token is automatically passed in as a part of the CI permissions model: https://docs.gitlab.com/ce/user/project/new_ci_build_permissions_model.html
This change will need applying to the GovCMS8 CI validation also.