Add keyword override and make method non-virtual

dune/solvers/solvers/quadraticipopt.hh

@@ -722,7 +722,7 @@ public:
       tolerance_ = tolerance;
     }
 
-    virtual void solve();
+    void solve() override;
 
 protected:
     ///////////////////////////////////////////////////////

dune/solvers/solvers/umfpacksolver.hh

@@ -65,7 +65,7 @@ public:
     rhs_ = &rhs;
   }
 
-  virtual void solve()
+  void solve() override
   {
     // We may use the original rhs, but ISTL modifies it, so we need a non-const type here
     VectorType mutableRhs = *rhs_;