chore(deps): Bump flake8 and pycodestyle

[cphoward]

Bumping TEST_DEPENDENCIES since importlib_metadata removed deprecated features.

[fantix]

Seems one of the test is hanging, I'll look into it later.

[cphoward]

Seems one of the test is hanging, I'll look into it later.

@fantix, it looks to be hanging in test_tcp.py, but only with Ubuntu. I've experimented with changing the Ubuntu version and skipping some tests, but the tests are still prohibitively slow. I've even just pinned importlib_metadata<4.3, that being the only change introduced to the master branch, and the Ubuntu tests still timeout. It seem something happened with the Ubuntu image.

[cphoward]

@elprans, This is a more up-to-date version of the changes you approved at #515.

[fantix]

Closing as #520 is merged.