YaspFixedSizePartioner broken after !607

The updates in !607 (merged) break downstream code

error: cannot declare variable ‘lb’ to be of abstract type ‘Dune::YaspFixedSizePartitioner<1>’
4  169 |             Dune::YaspFixedSizePartitioner<dim> lb(partitioning);
5      |                                                 ^~

/dune/modules/dune-grid/dune/grid/yaspgrid/partitioning.hh:237:84: error: type ‘Dune::YLoadBalanceForward<1>’ is not a direct base of ‘Dune::YaspFixedSizePartitioner<1>’
21  237 |       YLoadBalanceForward<d>(std::make_unique<Yasp::FixedSizePartitioning<d>>(dims))
22      |                                                                                    ^