$ git clone -n https://github.com/xcp-ng-rpms/xen /var/lib/mock/v8.3-incoming-9244-28016/root/chroot_tmpdir/scmroot/xen
Cloning into '/var/lib/mock/v8.3-incoming-9244-28016/root/chroot_tmpdir/scmroot/xen'...
$ git fetch origin 4a7c97472a99b15042c2f8c2817f0ebcafdb830f:KOJI_FETCH_HEAD
From https://github.com/xcp-ng-rpms/xen
 * [new ref]         4a7c97472a99b15042c2f8c2817f0ebcafdb830f -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 4a7c974 Merge branch 'XS-8.3' into 8.3-XS83-4.17.5-18