Debugger: Use override consistently

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

Change-Id: I6a20484716dc5bd84fe9592b40ae57be66fe32bf
Reviewed-by: hjk <hjk@qt.io>

src/plugins/debugger/watchhandler.h

@@ -60,7 +60,7 @@ class WatchHandler : public QObject
 
 public:
     explicit WatchHandler(DebuggerEngine *engine);
-    ~WatchHandler();
+    ~WatchHandler() override;
 
     WatchModelBase *model() const;