$ git clone -n https://github.com/xcp-ng-rpms/xs-opam-repo.git /var/lib/mock/v8.3-u-psafont2-9639-28361/root/chroot_tmpdir/scmroot/xs-opam-repo
Cloning into '/var/lib/mock/v8.3-u-psafont2-9639-28361/root/chroot_tmpdir/scmroot/xs-opam-repo'...
$ git fetch origin 199047844680c0cc9cb43b733df31ff238287fde:KOJI_FETCH_HEAD
From https://github.com/xcp-ng-rpms/xs-opam-repo
 * [new ref]         199047844680c0cc9cb43b733df31ff238287fde -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 1990478 bump release for test build