rpmname: fix use_new_versioning regex
    
    filippo.io/edwards25519 should be golang-filippo-edwards25519, not
    golang-filippo-edwards2551_9.
    
    Fixes: https://pagure.io/GoSIG/go2rpm/issue/37
    Relates: https://gitlab.com/fedora/sigs/go/go2rpm/-/commit/8b7ae828e5e4099069a7f1976e8d1c2a5ed9da3c