$ git clone -n https://github.com/xcp-ng-rpms/xs-opam-repo /var/lib/mock/v8.3-u-psafont1-10483-29045/root/chroot_tmpdir/scmroot/xs-opam-repo
Cloning into '/var/lib/mock/v8.3-u-psafont1-10483-29045/root/chroot_tmpdir/scmroot/xs-opam-repo'...
$ git fetch origin 8428c2bc79f31fe19c8c4928bbe5a20bb916739a:KOJI_FETCH_HEAD
From https://github.com/xcp-ng-rpms/xs-opam-repo
 * [new ref]         8428c2bc79f31fe19c8c4928bbe5a20bb916739a -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 8428c2b bump release for test build