heptapod-ci: also run tests for chg on python 2
I am not aware of any regular effort to run test with chg. So let's at least do it
here.
Differential Revision: https://phab.mercurial-scm.org/D8178
[tool.black]
line-length = 80
exclude = '''
build/
| wheelhouse/
| dist/
| packages/
| \.hg/
| \.mypy_cache/
| \.venv/
| mercurial/thirdparty/
'''
skip-string-normalization = true
quiet = true