run-tests: prevent race-condition when picking a channel
Before this, multiple jobs could search the list at the same time and pick the
same free channel.
We now project this search/assignment with a simple lock.
[build-system]
requires = ["setuptools", "wheel"]
[tool.black]
line-length = 80
exclude = '''
build/
| wheelhouse/
| dist/
| packages/
| \.hg/
| \.mypy_cache/
| \.venv/
| mercurial/thirdparty/
'''
skip-string-normalization = true
quiet = true