cran: Fix ListedOrigin visit type

CRAN origins must be loaded with the cran visit type and not the tar one.

This is the reason why the CRAN origins are marked as not visited in scheduler metrics.

It also means that CRAN origins currently do not get loaded in production as there is no scheduler task type named load-tar.

Related to swh-scheduler#3675 (closed)

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Migrated from D6539 (view on Phabricator)