migrations: Adapt according to latest storage revision_get api change
Related to T645
Test Plan
tox (possibly failing until swh.storage release > 0.13.3)
Migrated from D3864 (view on Phabricator)
Staging instance, all changes can be removed at any time
Related to T645
tox (possibly failing until swh.storage release > 0.13.3)
Migrated from D3864 (view on Phabricator)