Move project-specific pins out of upstream.

[jaraco]

• Move workaround for test_cygwin job failing after adding ruff #3921 to the local section, restoring upstream to match upstream.
• Exclude pytest-ruff (and thus ruff), which cannot build on cygwin.

Summary of changes

Closes

Pull Request Checklist

• Changes have tests
• News fragment added in newsfragments/.
  (See documentation for details)