tests: Explicit registering test tasks step for the swh_app
Prior to this commit, the celery "app" import changed. Making the runtime application load prior to the tests "swh_app". In effect, making the tasks not being consumed by workers.
This explicitely forces the tests tasks registering to "swh_app". In effect clarifying code and fixing the current tests.
Related swh-core!306 (closed) Related 8eafc70a
Test Plan
tox
Migrated from D2115 (view on Phabricator)