$ git clone -n https://github.com/xcp-ng-rpms/opam.git /var/lib/mock/v8.3-u-psafont2-9615-28352/root/chroot_tmpdir/scmroot/opam
Cloning into '/var/lib/mock/v8.3-u-psafont2-9615-28352/root/chroot_tmpdir/scmroot/opam'...
$ git fetch origin 1608cf554964ac5ec0687b388c1f38308f7972fa:KOJI_FETCH_HEAD
From https://github.com/xcp-ng-rpms/opam
 * [new ref]         1608cf554964ac5ec0687b388c1f38308f7972fa -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 1608cf5 bump release for test build