conda: Yield listed origins after all artifacts in a page are processed
swh-scheduler will deduplicate listed origins according to their URL and visit type but not according to their extra loader arguments.
Previously, listed origins were yielded after each processed artifact in a page so we could lose some package version info due to the deduplication process.
So ensure to yield listed origins once all artifacts in a page have been processed.
Migrated from D8747 (view on Phabricator)