messageList: Only close messages via delete key if they can be closed

If the delete key is pressed while a message/MPRIS indicator is focused
GNOME now asks whether the message/MPRIS indicator is closable.
If yes it will be closed but if not it won't be closed.

https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/5536

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2323>

js/ui/messageList.js

@@ -535,9 +535,11 @@ var Message = GObject.registerClass({
 
         if (keysym == Clutter.KEY_Delete ||
             keysym == Clutter.KEY_KP_Delete) {
+            if (this.canClose()) {
                 this.close();
                 return Clutter.EVENT_STOP;
             }
+        }
         return super.vfunc_key_press_event(keyEvent);
     }
 });