$ git clone -n https://github.com/xcp-ng-rpms/xen.git /var/lib/mock/v8.3-incoming-9345-28103/root/chroot_tmpdir/scmroot/xen
Cloning into '/var/lib/mock/v8.3-incoming-9345-28103/root/chroot_tmpdir/scmroot/xen'...
$ git fetch origin 03e798492e4421c8f26827d4afe4ec172670f20f:KOJI_FETCH_HEAD
From https://github.com/xcp-ng-rpms/xen
 * [new ref]         03e798492e4421c8f26827d4afe4ec172670f20f -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 03e7984 Merge pull request #69 from xcp-ng-rpms/8.3-XS83-4.17.5-18