pubdev: Modify loader after origin URL modification in related lister
Origin URL for a package listed by the pubdev lister is now in the form https://pub.dev/packages/<package_name> so we need to reconstruct the API URL to get package versions from it.
Related to T4465
Depends on swh-lister!443 (closed)
Migrated from D8355 (view on Phabricator)