$ git clone -n https://src.fedoraproject.org/rpms/jbig2dec.git /var/lib/mock/f40-build-2241322-53661/root/chroot_tmpdir/scmroot/jbig2dec
Cloning into '/var/lib/mock/f40-build-2241322-53661/root/chroot_tmpdir/scmroot/jbig2dec'...
$ git fetch origin ebef85e5aecef70e25331a24a1b98516691b58d9:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/jbig2dec
 * [new ref]         ebef85e5aecef70e25331a24a1b98516691b58d9 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at ebef85e rebase to 0.20 (rhbz#2238815)