Use TupleVector instead of MultiTypeBlockVector in conceptcheck.cc

Since recently, MultiTypeBlockVector tries to construct a common
field type from its entries, which makes it a bit more strict
in what it accepts as entries.  This makes conceptcheck.cc fail.

Since MultiTypeBlockVector is not actually needed here, simply
replace it by TupleVector, which is more forgiving.

dune/tnnmg/test/conceptcheck.cc

@@ -4,10 +4,10 @@
 
 #include <dune/common/concept.hh>
 #include <dune/common/fvector.hh>
+#include <dune/common/tuplevector.hh>
 #include <dune/common/typetraits.hh>
 
 #include <dune/istl/bvector.hh>
-#include <dune/istl/multitypeblockvector.hh>
 
 #include <dune/tnnmg/concepts.hh>
 
@@ -23,14 +23,14 @@ int main() {
   using CT1 = std::tuple<double, double>;
   using CT2 = std::tuple<double, std::string>;
   using CT3 = std::tuple<CT1, CT2>;
-  using CT4 = Dune::MultiTypeBlockVector<CT1, CT3>;
+  using CT4 = Dune::TupleVector<CT1, CT3>;
 
   using NCT0 = NonComparable;
   using NCT1 = std::complex<int>;
   using NCT2 = std::tuple<double, NonComparable>;
   using NCT3 = std::tuple<CT3, NCT1>;
   using NCT4 = std::tuple<NCT2, CT3>;
-  using NCT5 = Dune::MultiTypeBlockVector<CT1, NCT3>;
+  using NCT5 = Dune::TupleVector<CT1, NCT3>;
 
 
   // Check comparable types