$ git clone -n https://github.com/xcp-ng-rpms/xs-opam-repo.git /var/lib/mock/v8.3-u-psafont2-9717-28427/root/chroot_tmpdir/scmroot/xs-opam-repo
Cloning into '/var/lib/mock/v8.3-u-psafont2-9717-28427/root/chroot_tmpdir/scmroot/xs-opam-repo'...
$ git fetch origin b86274079fdc53882bb74f91043f18d24877e4d6:KOJI_FETCH_HEAD
From https://github.com/xcp-ng-rpms/xs-opam-repo
 * [new ref]         b86274079fdc53882bb74f91043f18d24877e4d6 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at b862740 bump release for test build