$ git clone -n https://src.fedoraproject.org/rpms/prooftree.git /var/lib/mock/f38-build-side-42-init-devel-789193-27976/root/chroot_tmpdir/scmroot/prooftree
Cloning into '/var/lib/mock/f38-build-side-42-init-devel-789193-27976/root/chroot_tmpdir/scmroot/prooftree'...
$ git fetch origin b35e08678c90ba5d6d732b303a07faf0283fce4d:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/prooftree
 * [new ref]         b35e08678c90ba5d6d732b303a07faf0283fce4d -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at b35e086 Rebuild OCaml packages for F38