refactor: free more reachable memory with EXITFREE (#26349)

Discovered using __sanitizer_print_memory_profile().

src/nvim/ui.c

@@ -134,6 +134,8 @@ void ui_free_all_mem(void)
     free_ui_event_callback(event_cb);
   })
   map_destroy(uint32_t, &ui_event_cbs);
+
+  multiqueue_free(resize_events);
 }
 #endif