$ git clone -n https://src.fedoraproject.org/rpms/R-diffobj.git /var/lib/mock/f40-build-1930477-25111/root/chroot_tmpdir/scmroot/R-diffobj
Cloning into '/var/lib/mock/f40-build-1930477-25111/root/chroot_tmpdir/scmroot/R-diffobj'...
$ git fetch origin 23b64539072709a1436415d6318900e769611d49:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/R-diffobj
 * [new ref]         23b64539072709a1436415d6318900e769611d49 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 23b6453 R-maint-sig mass rebuild