swh.web.tests: Adapt get_indexer_storage to latest version
Related to D4272
Test Plan
tox (failing until swh.indexer > 3.0)
Migrated from D4275 (view on Phabricator)
Staging instance, all changes can be removed at any time
Related to D4272
tox (failing until swh.indexer > 3.0)
Migrated from D4275 (view on Phabricator)