metadata: Adapt to latest storage revision_get change
Related to T645
Test Plan
tox (failing until swh.storage release > 0.13.3)
Migrated from D3865 (view on Phabricator)
Staging instance, all changes can be removed at any time
Related to T645
tox (failing until swh.storage release > 0.13.3)
Migrated from D3865 (view on Phabricator)