CppTools: Use override consistently

clang-tidy fixes from modernize-use-override check.

Change-Id: I0e6d6a9df3e87b8042ccc5ea0adc70070a3821d6
Reviewed-by: Ivan Donchevskii <ivan.donchevskii@qt.io>

src/plugins/cpptools/cpprefactoringchanges.h

@@ -72,7 +72,7 @@ protected:
     CppRefactoringFile(TextEditor::TextEditorWidget *editor);
 
     CppRefactoringChangesData *data() const;
-    virtual void fileChanged();
+    void fileChanged() override;
 
     mutable CPlusPlus::Document::Ptr m_cppDocument;