Update bresser_weather_station.yaml

In some weather conditions `Heat index` doesn't available and weather display show it's as `Lo`.

custom_components/tuya_local/devices/bresser_weather_station.yaml

@@ -312,6 +312,7 @@ secondary_entities:
     class: temperature
     dps:
       - id: 66
+        optional: true
         <<: *temperature
   - entity: sensor
     name: Wind chill index