tests: Use 'offset_bytes' instead of 'offset'/'negative_utc'
Change required by swh-model 5.0.0
Test Plan
Will fail because this depends on swh-model!313 (closed), which isn't released yet.
Migrated from D6940 (view on Phabricator)
Change required by swh-model 5.0.0
Will fail because this depends on swh-model!313 (closed), which isn't released yet.
Migrated from D6940 (view on Phabricator)