$ git clone -n https://github.com/xcp-ng-rpms/xen /var/lib/mock/v8.3-u-tae1-10209-28783/root/chroot_tmpdir/scmroot/xen
Cloning into '/var/lib/mock/v8.3-u-tae1-10209-28783/root/chroot_tmpdir/scmroot/xen'...
$ git fetch origin c5c874debe92f109fd72a6e1326581f0886d5ae5:KOJI_FETCH_HEAD
From https://github.com/xcp-ng-rpms/xen
 * [new ref]         c5c874debe92f109fd72a6e1326581f0886d5ae5 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at c5c874d bump release for test build