Move temperature conversions to sensor base class (3/8) (#54469)

* Move temperature conversions to entity base class (3/8)

* Fix FritzBox sensor

* Fix tests

homeassistant/components/gtfs/sensor.py

@@ -559,7 +559,7 @@ class GTFSDepartureSensor(SensorEntity):
         return self._name
 
     @property
-    def state(self) -> str | None:  # type: ignore
+    def native_value(self) -> str | None:  # type: ignore
         """Return the state of the sensor."""
         return self._state