$ git clone -n https://github.com/xcp-ng-rpms/xen.git /var/lib/mock/v8.3-incoming-10125-28716/root/chroot_tmpdir/scmroot/xen
Cloning into '/var/lib/mock/v8.3-incoming-10125-28716/root/chroot_tmpdir/scmroot/xen'...
$ git fetch origin c091f8ff6a61fdc62f87491ce216c05a0a605150:KOJI_FETCH_HEAD
From https://github.com/xcp-ng-rpms/xen
 * [new ref]         c091f8ff6a61fdc62f87491ce216c05a0a605150 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at c091f8f Rebuild with python-3 (with openssl-3)