Fix modbus boolean decoding

Summary

When reading a bool value from a modbus node as discrete input, an error is raised.

Explain your context

I was trying to read whether a phase on an emonio device was connected

Was there an error message?

val = struct.unpack(unpack, struct.pack(pack, *value))[0]
struct.error: unpack requires a buffer of 1 bytes

Steps to reproduce

(How one can reproduce the issue - this is very important)

import struct

value = [1]
dtype = "?"
_len=1
bo=">"
pack = f">{len(value):1d}H"
unpack = f"{bo}{_len}{dtype}"

# Convert the value into the appropriate format
val = struct.unpack(unpack, struct.pack(pack, *value))[0]