LibWeb: Apply suggested fixes.

Author: https://github.com/asynts
Commit: 2981f10a5e
Pull-request: https://github.com/SerenityOS/serenity/pull/4318
Reviewed-by: https://github.com/Lubrsi
Reviewed-by: https://github.com/awesomekling
Reviewed-by: https://github.com/linusg

Libraries/LibWeb/CodeGenerators/WrapperGenerator.cpp

@@ -476,9 +476,8 @@ public:
     }
 
     generator.append(R"~~~(
-    virtual bool is_@wrapper_class:snakecase@() const final { return true; }
-
 private:
+    virtual bool is_@wrapper_class:snakecase@() const final { return true; }
 )~~~");
 
     for (auto& function : interface.functions) {