$ git clone -n https://github.com/xcp-ng-rpms/xs-opam-repo.git /var/lib/mock/v8.3-u-psafont2-9757-28474/root/chroot_tmpdir/scmroot/xs-opam-repo
Cloning into '/var/lib/mock/v8.3-u-psafont2-9757-28474/root/chroot_tmpdir/scmroot/xs-opam-repo'...
$ git fetch origin 619738ed798264a8b279738e7902771377a8e4dc:KOJI_FETCH_HEAD
From https://github.com/xcp-ng-rpms/xs-opam-repo
 * [new ref]         619738ed798264a8b279738e7902771377a8e4dc -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 619738e bump release for test build