vfs: suppress some pytype errors around us using a private attribute
Looking at threading._MainThread seems like we're probably a little
unsupported, but since this code appears to work on both Python 2 and
3 I'm not going to sweat this for now.
Differential Revision: https://phab.mercurial-scm.org/D7282
[tool.black]
line-length = 80
exclude = '''
build/
| wheelhouse/
| dist/
| packages/
| \.hg/
| \.mypy_cache/
| \.venv/
| mercurial/thirdparty/
| contrib/python-zstandard/
'''
skip-string-normalization = true
quiet = true