simpletest example not handling in_channel tuples

[caternuson]

Re this thread:
https://forums.adafruit.com/viewtopic.php?f=60&t=176352#p859127

in_channel can be a tuple, which the example code does not handle:

Adafruit_CircuitPython_MIDI/examples/midi_simpletest.py

Lines 20 to 23 in 41b021b

	print(
	"Listening on input channel:",
	midi.in_channel + 1 if midi.in_channel is not None else None,
	)