Correct max. read size for registers. (#2295)

pymodbus/pdu/register_read_message.py

@@ -89,7 +89,7 @@ def decode(self, data):
         :param data: The request to decode
         """
         byte_count = int(data[0])
-        if byte_count < 2 or byte_count > 246 or byte_count % 2 == 1 or byte_count != len(data) - 1:
+        if byte_count < 2 or byte_count > 252 or byte_count % 2 == 1 or byte_count != len(data) - 1:
             raise ModbusIOException(f"Invalid response {data} has byte count of {byte_count}")
         self.registers = []
         for i in range(1, byte_count + 1, 2):