Update plugin_growatt.py add serial number for GEN3 inverters

Additional code to find serial number for GEN3 inverters using register 209

Author: brad5505

custom_components/solax_modbus/plugin_growatt.py

@@ -9498,6 +9498,9 @@ class growatt_plugin(plugin_base):
     async def async_determineInverterType(self, hub, configdict):
         _LOGGER.info(f"{hub.name}: trying to determine inverter type")
         seriesnumber = await async_read_serialnr(hub, 3001)
+        if not seriesnumber:
+            _LOGGER.info(f"{hub.name}: trying alternative location")
+            seriesnumber = await async_read_serialnr(hub, 209)
         if not seriesnumber:
             _LOGGER.info(f"{hub.name}: trying alternative location")
             seriesnumber = await async_read_serialnr(hub, 9)