Core: Use override consistently

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

Change-Id: If33399d60e96cae766bbedbe30044ada411e862f
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/coreplugin/modemanager.h

@@ -68,7 +68,7 @@ signals:
 
 private:
     explicit ModeManager(Internal::MainWindow *mainWindow, Internal::FancyTabWidget *modeStack);
-    ~ModeManager();
+    ~ModeManager() override;
 
     static void extensionsInitialized();