Fix C.120 good example (#1426)

C.120 has a good example which violates C.128 by specifying both virtual and override for methods.
closes #1425

CppCoreGuidelines.md

@@ -6788,8 +6788,8 @@ Do *not* use inheritance when simply having a data member will do. Usually this
     };
 
     class PushButton : public AbstractButton {
-        virtual void render() const override;
-        virtual void onClick() override;
+        void render() const override;
+        void onClick() override;
         // ...
     };