Investigate Python 3.8 windows test failure

This was from unrelated code change:

```
_____________________________ test_interval_timer _____________________________

def test_interval_timer():
func = mock.Mock()
timer = IntervalTimer(function=func, interval=0.1, args=(1,), kwargs={"a": "b"})
timer.start()
time.sleep(0.25)
try:
> assert func.call_count == 2
E AssertionError: assert 1 == 2
E + where 1 = .call_count

tests\utils\threading_tests.py:46: AssertionError
```

Start with tests/utils/threading_tests.py and the test_interval_timer failure shown in the report, then run that test on Windows with Python 3.8. Trace the IntervalTimer behavior around the 0.1-second interval and the expected two calls. Done means the cause of the platform-specific failure is identified and the test or implementation has a verified resolution.

Written by the indexing model from the issue text.