hypothesis: Fix or ignore deprecation warnings since version 5.6
Since version 5.6, hypothesis warns on @given + function-scoped fixtures
(discussion about the legibility of that change here).
As a consequence a LOT of warnings are now issued when running swh-web tests,
see https://jenkins.softwareheritage.org/job/DWAPPS/job/tests-on-diff/29/console
for instance.
So turns concerned swh-web fixtures from function-scoped to module-scoped
(there is strictly no difference in tests execution result after that change)
and ignore some warnings related to external function-scoped fixtures that
are safe to use with @given (client from pytest-django and mocker from
pytest-mock).
Migrated from D2933 (view on Phabricator)