Owon PCT513: use new preheating hvac_action

A few versions back, HA added preheating to the possible hvac_actions.
This device had already added a preheating state as heating in #616

custom_components/tuya_local/devices/owon_pct513_thermostat.yaml

@@ -157,7 +157,7 @@ primary_entity:
         - dps_val: heatfanon
           value: heating
         - dps_val: "1"
-          value: heating
+          value: preheating
 secondary_entities:
   - entity: number
     name: Fan runtime