Disable timing tests on pypy
Disable timing tests on pypy

Doing timing tests on pypy (for blink) just doesn't work; even with a
tolerance as coarse as tens-of-milliseconds, things fail. I guess that
isn't too surprising given that, as the tests are one off things the
pypy JIT is never getting a chance to spin up and do its stuff.

waveform80/gpio-zero,MrHarcombe/python-gpiozero,lurch/python-gpiozero,RPi-Distro/python-gpiozero