Remove unneeded type checking from Sensibo (#85231)

homeassistant/components/sensibo/sensor.py

@@ -352,8 +352,6 @@ class SensiboDeviceSensor(SensiboDeviceBaseEntity, SensorEntity):
     def native_value(self) -> StateType | datetime:
         """Return value of sensor."""
         state = self.entity_description.value_fn(self.device_data)
-        if isinstance(state, str):
-            return state.lower()
         return state
 
     @property