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/icore.h

@@ -58,7 +58,7 @@ class CORE_EXPORT ICore : public QObject
     friend class IWizardFactory;
 
     explicit ICore(Internal::MainWindow *mw);
-    ~ICore();
+    ~ICore() override;
 
 public:
     enum class ContextPriority {