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)
Staging instance, all changes can be removed at any time
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)