Help: Use override consistently

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

Change-Id: I3aec6d7ab1e8f088b745d2d9730e3d49ced42031
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/help/openpageswidget.h

@@ -38,7 +38,7 @@ class OpenPagesWidget : public Core::OpenDocumentsTreeView
 
 public:
     explicit OpenPagesWidget(OpenPagesModel *model, QWidget *parent = nullptr);
-    ~OpenPagesWidget();
+    ~OpenPagesWidget() override;
 
     void selectCurrentPage();
     void allowContextMenu(bool ok);