$ git clone -n https://github.com/xcp-ng-rpms/xcp-emu-manager.git /var/lib/mock/v8.3-incoming-9937-28628/root/chroot_tmpdir/scmroot/xcp-emu-manager
Cloning into '/var/lib/mock/v8.3-incoming-9937-28628/root/chroot_tmpdir/scmroot/xcp-emu-manager'...
$ git fetch origin ce20f6c94c76947791a1ff128823f3475ffd9193:KOJI_FETCH_HEAD
From https://github.com/xcp-ng-rpms/xcp-emu-manager
 * [new ref]         ce20f6c94c76947791a1ff128823f3475ffd9193 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at ce20f6c updated spec + new source