Re-add group polling as a fallback for observation (#13613)

homeassistant/components/light/tradfri.py

@@ -76,11 +76,6 @@ class TradfriGroup(Light):
         """Return unique ID for this group."""
         return self._unique_id
 
-    @property
-    def should_poll(self):
-        """No polling needed for tradfri group."""
-        return False
-
     @property
     def supported_features(self):
         """Flag supported features."""
@@ -149,6 +144,10 @@ class TradfriGroup(Light):
         self._refresh(tradfri_device)
         self.async_schedule_update_ha_state()
 
+    async def async_update(self):
+        """Fetch new state data for the group."""
+        await self._group.update()
+
 
 class TradfriLight(Light):
     """The platform class required by Home Assistant."""