$ git clone -n https://src.fedoraproject.org/rpms/mutter.git /var/lib/mock/f39-build-1701798-41210/root/chroot_tmpdir/scmroot/mutter
Cloning into '/var/lib/mock/f39-build-1701798-41210/root/chroot_tmpdir/scmroot/mutter'...
$ git fetch origin 78df570c6c8973e49bc94ae495d247524a427ec3:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/mutter
 * [new ref]         78df570c6c8973e49bc94ae495d247524a427ec3 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 78df570 Update to 45.1