tests: conditionalize `chmod` usage in `test-upgrade-repo.t`
While the command itself doesn't error out on Windows, it also doesn't make the
filesystem readonly. Therefore the repo gets altered to drop dirstate-v2, and
puts it out of sync with that happens on Linux.
[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