$ git clone -n https://github.com/xcp-ng-rpms/opam.git /var/lib/mock/v8.3-incoming-9783-28498/root/chroot_tmpdir/scmroot/opam
Cloning into '/var/lib/mock/v8.3-incoming-9783-28498/root/chroot_tmpdir/scmroot/opam'...
$ git fetch origin 08f0029bdfbeba0eaf5dab02e54f5328cec253c9:KOJI_FETCH_HEAD
From https://github.com/xcp-ng-rpms/opam
 * [new ref]         08f0029bdfbeba0eaf5dab02e54f5328cec253c9 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 08f0029 Update opam to 2.4.1 (#2)