Tests hang on Python 3.9+ due to thread ident being clobbered

[gpshead]

This line https://github.com/alexmojaki/snoop/blob/v0.4.1/tests/test_snoop.py#L26 isn't safe to do to Python.

tox -e py39 hangs when it should be exiting pytest as a result.

Any of the tests/sample_results/ files containing a thread id need to be pre-processed to insert the actual live thread id from the test instead if you want to do == comparisons on them

[alexmojaki]

Thank you, I didn't even realise I had a failing build badge! Fixed in 16f32ce