test_init: Fix tests using the latest swh-storage fixture

Fixes both master and debian builds [1] [2] (which are now the same, progress!)

• [1] https://jenkins.softwareheritage.org/job/DLDBASE/job/tests/lastBuild/console

• [2] https://jenkins.softwareheritage.org/view/Debian%20packages/job/debian/job/packages/job/DLDBASE/job/gbp-buildpackage/155/console

Test Plan

tox

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Migrated from D3531 (view on Phabricator)