Compiler error Dune 2.6 with clang 10

I get a compiler error with clang 10 here:

dune-istl/dune/istl/owneroverlapcopy.hh:292:18: error: assigning to 'SolverCategory::Category' from incompatible type 'Dune::SolverCategory'
      category = set;
                 ^~~

I wonder how this could ever work? Fix in !389 (merged).