Avatto TRV06: update unit on calibration

- if C or F is used for relative temperatures, HA "converts" them when the user's temperature unit setting is different, which is wrong, because C to F conversion is not just scaling but a range shift as well. So relative temperatures such as calibration offset have to be in degrees without specifying the scale.

custom_components/tuya_local/devices/avatto_trv06_radiatorvalve.yaml

@@ -99,7 +99,7 @@ secondary_entities:
         type: integer
         optional: true
         name: value
-        unit: C
+        unit: °
         range:
           min: -9
           max: 9