Meaco Arete Two: make mode optional

12L model is not reporting mode (may be a temporary state the device is in
and may also happen with other size models).

Issue #2626

custom_components/tuya_local/devices/meaco_aretetwo_dehumidifier.yaml

@@ -20,6 +20,7 @@ primary_entity:
     - id: 4
       name: mode
       type: string
+      optional: true
       mapping:
         - dps_val: manual
           value: normal