debian/gbp-buildpackage: Use mirror of cassandra debian repository
Main apache repository is no longer reachable from our infra so we need to use a mirror to fetch cassandra package now.
Migrated from D8743 (view on Phabricator)
Main apache repository is no longer reachable from our infra so we need to use a mirror to fetch cassandra package now.
Migrated from D8743 (view on Phabricator)