Debugger: Use override consistently

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

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

src/plugins/debugger/debuggerplugin.h

@@ -40,7 +40,7 @@ class DebuggerPlugin : public ExtensionSystem::IPlugin
 
 public:
     DebuggerPlugin();
-    ~DebuggerPlugin();
+    ~DebuggerPlugin() override;
 
     static DebuggerPlugin *instance();