$ git clone -n https://github.com/xcp-ng-rpms/xen.git /var/lib/mock/v8.3-incoming-9805-28521/root/chroot_tmpdir/scmroot/xen
Cloning into '/var/lib/mock/v8.3-incoming-9805-28521/root/chroot_tmpdir/scmroot/xen'...
$ git fetch origin 09aa073cda42059af2ede8599be0e59aaa1bc872:KOJI_FETCH_HEAD
From https://github.com/xcp-ng-rpms/xen
 * [new ref]         09aa073cda42059af2ede8599be0e59aaa1bc872 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 09aa073 Merge branch 'XS-8.3' into 8.3-import_xen-4.17.5-23.xs8.src.rpm