fix runtime with pymodbus>=3.7.0

https://github.com/nmakel/solaredge_modbus/pull/103
Index: src/solaredge_modbus/__init__.py
--- src/solaredge_modbus/__init__.py.orig
+++ src/solaredge_modbus/__init__.py
@@ -6,7 +6,7 @@ from pymodbus.payload import BinaryPayloadBuilder
 from pymodbus.payload import BinaryPayloadDecoder
 from pymodbus.client import ModbusTcpClient
 from pymodbus.client import ModbusSerialClient
-from pymodbus.register_read_message import ReadHoldingRegistersResponse
+from pymodbus.pdu.register_read_message import ReadHoldingRegistersResponse
 
 
 RETRIES = 3
