$ git clone -n https://src.fedoraproject.org/rpms/system-rules.git /var/lib/mock/f40-build-1884356-25049/root/chroot_tmpdir/scmroot/system-rules
Cloning into '/var/lib/mock/f40-build-1884356-25049/root/chroot_tmpdir/scmroot/system-rules'...
$ git fetch origin 17c82dd5741f3909dc1a12372a06d2abb615dbc2:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/system-rules
 * [new ref]         17c82dd5741f3909dc1a12372a06d2abb615dbc2 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 17c82dd Merge branch 'rawhide' into f40