$ git clone -n https://src.fedoraproject.org/rpms/mathjax3.git /var/lib/mock/f40-build-2153517-50914/root/chroot_tmpdir/scmroot/mathjax3
Cloning into '/var/lib/mock/f40-build-2153517-50914/root/chroot_tmpdir/scmroot/mathjax3'...
$ git fetch origin b73a6000406a1a0a18c45cde314d0a2dc60c5de3:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/mathjax3
 * [new ref]         b73a6000406a1a0a18c45cde314d0a2dc60c5de3 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at b73a600 Correct license tag (rhbz#2244891)