$ git clone -n https://github.com/xcp-ng-rpms/opam.git /var/lib/mock/v8.3-u-psafont2-9743-28450/root/chroot_tmpdir/scmroot/opam
Cloning into '/var/lib/mock/v8.3-u-psafont2-9743-28450/root/chroot_tmpdir/scmroot/opam'...
$ git fetch origin 837b0792adabd9de40aae036a72f2bee2e7c22a3:KOJI_FETCH_HEAD
From https://github.com/xcp-ng-rpms/opam
 * [new ref]         837b0792adabd9de40aae036a72f2bee2e7c22a3 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 837b079 bump release for test build