python bindings for UGGrid broken

The python bindings for UGGrid currently fail to compile, which leads to the interpreter getting stuck (see dune-common#288 (closed))

dune/grid/uggrid/uggridleafiterator.hh:150:20: error: no matching function for call to ‘Dune::UGGridLeafIterator<1, Dune::Interior_Partition, const Dune::UGGrid<2> >::isLeaf(Dune::UG_NS<2>::Entity<1>::T*)’
  150 |       return isLeaf(entity_.impl().getTarget());

I guess there is an error in the handling of capabilities... Note that having entities does not imply that the corresponding iterator is present.