$ git clone -n https://src.fedoraproject.org/rpms/mathjax3.git /var/lib/mock/f45-build-18116-508/root/chroot_tmpdir/scmroot/mathjax3
Cloning into '/var/lib/mock/f45-build-18116-508/root/chroot_tmpdir/scmroot/mathjax3'...
$ git fetch origin f332112d7d755f6e10b5b644c5d93e06983577d7:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/mathjax3
 * [new ref]         f332112d7d755f6e10b5b644c5d93e06983577d7 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at f332112 Rebuilt for https://fedoraproject.org/wiki/Fedora_45_Mass_Rebuild