loader: Adapt to swh-model >= 0.4.0
extra_headers is now a top-level attribute of a Revision and its type has changed to Tuple[Tuple[bytes, bytes], ...].
Related to swh-model#2423 (closed)
Migrated from D3463 (view on Phabricator)
extra_headers is now a top-level attribute of a Revision and its type has changed to Tuple[Tuple[bytes, bytes], ...].
Related to swh-model#2423 (closed)
Migrated from D3463 (view on Phabricator)