$ git clone -n https://src.fedoraproject.org/rpms/f41-backgrounds.git /var/lib/mock/f42-build-3272222-41305/root/chroot_tmpdir/scmroot/f41-backgrounds
Cloning into '/var/lib/mock/f42-build-3272222-41305/root/chroot_tmpdir/scmroot/f41-backgrounds'...
$ git fetch origin cec909fa6b3857df027dc92e9dc27dab127f4b3f:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/f41-backgrounds
 * [new ref]         cec909fa6b3857df027dc92e9dc27dab127f4b3f -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at cec909f New release removing alpha channel for PNG images