$ git clone -n https://github.com/xcp-ng-rpms/xs-opam-repo.git /var/lib/mock/v8.3-u-psafont2-9621-28352/root/chroot_tmpdir/scmroot/xs-opam-repo
Cloning into '/var/lib/mock/v8.3-u-psafont2-9621-28352/root/chroot_tmpdir/scmroot/xs-opam-repo'...
$ git fetch origin 3c7dc2a70999888cce3eed4608badbeb0dcfe79f:KOJI_FETCH_HEAD
From https://github.com/xcp-ng-rpms/xs-opam-repo
 * [new ref]         3c7dc2a70999888cce3eed4608badbeb0dcfe79f -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 3c7dc2a bump release for test build