Update dependency flake8 to v4

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
flake8 (changelog)	==3.8.3 -> ==4.0.1

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Release Notes

pycqa/flake8

### [`v4.0.1`](https://togithub.com/pycqa/flake8/compare/4.0.0...4.0.1) [Compare Source](https://togithub.com/pycqa/flake8/compare/4.0.0...4.0.1) ### [`v4.0.0`](https://togithub.com/pycqa/flake8/compare/3.9.2...4.0.0) [Compare Source](https://togithub.com/pycqa/flake8/compare/3.9.2...4.0.0) ### [`v3.9.2`](https://togithub.com/pycqa/flake8/compare/3.9.1...3.9.2) [Compare Source](https://togithub.com/pycqa/flake8/compare/3.9.1...3.9.2) ### [`v3.9.1`](https://togithub.com/pycqa/flake8/compare/3.9.0...3.9.1) [Compare Source](https://togithub.com/pycqa/flake8/compare/3.9.0...3.9.1) ### [`v3.9.0`](https://togithub.com/pycqa/flake8/compare/3.8.4...3.9.0) [Compare Source](https://togithub.com/pycqa/flake8/compare/3.8.4...3.9.0) ### [`v3.8.4`](https://togithub.com/pycqa/flake8/compare/3.8.3...3.8.4) [Compare Source](https://togithub.com/pycqa/flake8/compare/3.8.3...3.8.4)

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