$ git clone -n https://github.com/xcp-ng-rpms/xen.git /var/lib/mock/v8.3-incoming-9809-28521/root/chroot_tmpdir/scmroot/xen
Cloning into '/var/lib/mock/v8.3-incoming-9809-28521/root/chroot_tmpdir/scmroot/xen'...
$ git fetch origin d8ce245682e438be93dec5373edab291e9ea03c3:KOJI_FETCH_HEAD
From https://github.com/xcp-ng-rpms/xen
 * [new ref]         d8ce245682e438be93dec5373edab291e9ea03c3 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at d8ce245 Merge branch 'XS-8.3' into 8.3-import_xen-4.17.5-23.xs8.src.rpm