$ git clone -n https://github.com/xcp-ng-rpms/xs-opam-repo.git /var/lib/mock/v8.3-u-prebuild-9272-28052/root/chroot_tmpdir/scmroot/xs-opam-repo
Cloning into '/var/lib/mock/v8.3-u-prebuild-9272-28052/root/chroot_tmpdir/scmroot/xs-opam-repo'...
$ git fetch origin 4f8012f741b986efb3ebc8eec97c40df97a5ae84:KOJI_FETCH_HEAD
From https://github.com/xcp-ng-rpms/xs-opam-repo
 * [new ref]         4f8012f741b986efb3ebc8eec97c40df97a5ae84 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 4f8012f bump release for test build