ignore no size changes

Author: willmcgugan

src/textual/app.py

@@ -4313,6 +4313,8 @@ async def _on_key(self, event: events.Key) -> None:
 
     async def _on_resize(self, event: events.Resize) -> None:
         event.stop()
+        if self._size is not None and self._size == event.size:
+            return
         self._size = event.size
         self._resize_event = event
         if self._resize_timer is None: