GToolBar: Make add_action() take a GAction& instead of NonnullRefPtr&&.

There's very little reason to take NonnullRefPtr&& in arguments really.
You can avoid ref-count churn in the cases where ownership is transferred
from the caller to the callee, but that's a pretty unusual situation and
not worth optimizing for at this stage.

Libraries/LibGUI/GToolBar.h

@@ -9,7 +9,7 @@ public:
     explicit GToolBar(GWidget* parent);
     virtual ~GToolBar() override;
 
-    void add_action(NonnullRefPtr<GAction>&&);
+    void add_action(GAction&);
     void add_separator();
 
     bool has_frame() const { return m_has_frame; }