Research registry DB server connection errors in staging

Sentry error: (source)

unknown: unknown error: scanning repository: failed to connect to `host=pgbouncer-registry.int.gstg.gitlab.net user=gitlab-registry database=gitlabhq_registry`: server error (ERROR: pgbouncer cannot connect to server (SQLSTATE 08P01))

Another error: https://sentry.gitlab.net/gitlab/container-registry/issues/2803258/?environment=gstg