Update flake8 requirement from ~=3.9 to ~=4.0 (#66)
Update flake8 requirement from ~=3.9 to ~=4.0 (#66)

Updates the requirements on [flake8](https://github.com/pycqa/flake8) to permit the latest version.
- [Release notes](https://github.com/pycqa/flake8/releases)
- [Commits](https://github.com/pycqa/flake8/compare/3.9.0...4.0.0)

---
updated-dependencies:
- dependency-name: flake8
  dependency-type: direct:production
...

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kyhau/reko