Fix unknown values in onewire (#113731)

* Fix unknown values in onewire

* Update tests

homeassistant/components/onewire/binary_sensor.py

@@ -143,6 +143,8 @@ class OneWireBinarySensor(OneWireEntity, BinarySensorEntity):
     entity_description: OneWireBinarySensorEntityDescription
 
     @property
-    def is_on(self) -> bool:
+    def is_on(self) -> bool | None:
         """Return true if sensor is on."""
+        if self._state is None:
+            return None
         return bool(self._state)