tests: use stock pytest_postgresql postgresql factory function
instead of (soon-to-be-deprecated) swh-core's postgresql_fact one.
Migrated from D7919 (view on Phabricator)
Staging instance, all changes can be removed at any time
instead of (soon-to-be-deprecated) swh-core's postgresql_fact one.
Migrated from D7919 (view on Phabricator)