$ git clone -n https://github.com/xcp-ng-rpms/xs-opam-repo.git /var/lib/mock/v8.3-u-psafont2-9645-28361/root/chroot_tmpdir/scmroot/xs-opam-repo
Cloning into '/var/lib/mock/v8.3-u-psafont2-9645-28361/root/chroot_tmpdir/scmroot/xs-opam-repo'...
$ git fetch origin cc0e0b9454998f943cfe7bcdea566acb04383968:KOJI_FETCH_HEAD
From https://github.com/xcp-ng-rpms/xs-opam-repo
 * [new ref]         cc0e0b9454998f943cfe7bcdea566acb04383968 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at cc0e0b9 bump release for test build