Make the prepare_event helper function pre-aggregate the events with same url
and strip these urls as well.
It makes no sense to register 2 different URLs when they are equal to a trailing ws detail. As a result, we must preaggregate them because the swh_cache_put() sql function won't allow several 'on conflict' for the same id.
Rewrite updater/test_backend.py with pytest and use the postgresql fixture
Migrated from D1035 (view on Phabricator)