$ git clone -n https://github.com/xcp-ng-rpms/xs-opam-repo.git /var/lib/mock/v8.3-v-qcow2-9063-27925/root/chroot_tmpdir/scmroot/xs-opam-repo
Cloning into '/var/lib/mock/v8.3-v-qcow2-9063-27925/root/chroot_tmpdir/scmroot/xs-opam-repo'...
$ git fetch origin 12369facdf80017aacbd07cf71b3fd6ddeeeda75:KOJI_FETCH_HEAD
From https://github.com/xcp-ng-rpms/xs-opam-repo
 * [new ref]         12369facdf80017aacbd07cf71b3fd6ddeeeda75 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 12369fa Rebuild xs-opam