$ git clone -n https://src.fedoraproject.org/rpms/php-swiftmailer6.git /var/lib/mock/f41-build-side-1-2753434-31224/root/chroot_tmpdir/scmroot/php-swiftmailer6
Cloning into '/var/lib/mock/f41-build-side-1-2753434-31224/root/chroot_tmpdir/scmroot/php-swiftmailer6'...
$ git fetch origin b9205247057cc10fb29f7e3d8c7c83d345fc23a2:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/php-swiftmailer6
 * [new ref]         b9205247057cc10fb29f7e3d8c7c83d345fc23a2 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at b920524 deprecated and FTBFS