$ git clone -n https://src.fedoraproject.org/rpms/glibmm2.68.git /var/lib/mock/f41-build-side-1-2646702-27247/root/chroot_tmpdir/scmroot/glibmm2.68
Cloning into '/var/lib/mock/f41-build-side-1-2646702-27247/root/chroot_tmpdir/scmroot/glibmm2.68'...
$ git fetch origin 9dcab44926c76fb31014b735a4a1cbeb90aceed8:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/glibmm2.68
 * [new ref]         9dcab44926c76fb31014b735a4a1cbeb90aceed8 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 9dcab44 Require libsigc++30 and not 20