$ git clone -n https://src.fedoraproject.org/rpms/timg.git /var/lib/mock/f42-build-side-1-3555749-46656/root/chroot_tmpdir/scmroot/timg
Cloning into '/var/lib/mock/f42-build-side-1-3555749-46656/root/chroot_tmpdir/scmroot/timg'...
$ git fetch origin 2fb4d025d73584c89eca0a62c6305e77c8d591d0:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/timg
 * [new ref]         2fb4d025d73584c89eca0a62c6305e77c8d591d0 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 2fb4d02 Update to 1.6.2