⬆ Update flake8 requirement from ^3.9.2 to ^5.0.4 (#396)

⬆ Update flake8 requirement from ^3.9.2 to ^5.0.4 (#396)

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/3.9.2...5.0.4)

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

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Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Sebastián Ramírez <tiangolo@gmail.com>