Cygwin tests started failing

[jaraco]

Sometime in the last month, the cygwin tests started failing. Error message is:

Run tox
Traceback (most recent call last):
  File "/usr/bin/tox", line 5, in <module>
    from tox.run import run
  File "/usr/lib/python3.9/site-packages/tox/__init__.py", line 3, in <module>
    from .run import main
  File "/usr/lib/python3.9/site-packages/tox/run.py", line 12, in <module>
    from tox.config.cli.parse import get_options
  File "/usr/lib/python3.9/site-packages/tox/config/cli/parse.py", line 11, in <module>
    from tox.config.source import Source, discover_source
  File "/usr/lib/python3.9/site-packages/tox/config/source/__init__.py", line 4, in <module>
    from .discover import discover_source
  File "/usr/lib/python3.9/site-packages/tox/config/source/discover.py", line 10, in <module>
    from .legacy_toml import LegacyToml
  File "/usr/lib/python3.9/site-packages/tox/config/source/legacy_toml.py", line 8, in <module>
    import tomli as tomllib
ModuleNotFoundError: No module named 'tomli'

It seems that there's a glitch in the cygwin package manager that it's not supplying this required package.

[jaraco]

This appears to be the same issue reported in pypa/setuptools#4831, which was fixed by pip-installing tox.

[jaraco]

I used git to cherry-pick the fix from setuptools.

git cherry-pick ba24375 -m 1

There's already a lot of variance between Setuptools' and distutils' cygwin routines, but I just resolved the conflicts as minimally as possible.

[jaraco]

Cherry-picking that change seems to have done the trick.