$ git clone -n https://src.fedoraproject.org/rpms/xorg-x11-xdm.git /var/lib/mock/f40-build-2648458-66779/root/chroot_tmpdir/scmroot/xorg-x11-xdm
Cloning into '/var/lib/mock/f40-build-2648458-66779/root/chroot_tmpdir/scmroot/xorg-x11-xdm'...
$ git fetch origin a82f2c54ea81533e92b7dd4eeccb09b8726af35a:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/xorg-x11-xdm
 * [new ref]         a82f2c54ea81533e92b7dd4eeccb09b8726af35a -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at a82f2c5 add back the & operator