MRC Magnum: make flooring type optional

Issue #1899

custom_components/tuya_local/devices/mrc_magnum_floorheater.yaml

@@ -359,6 +359,7 @@ secondary_entities:
       - id: 124
         type: string
         name: option
+        optional: true
         mapping:
           - dps_val: wood
             value: Wood