Update dependency flake8 to v4 - autoclosed

This MR contains the following updates:

Package	Type	Update	Change
flake8 (changelog)	dev-dependencies	major	^3.7.9 -> ^4.0.0

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Release Notes

pycqa/flake8

v4.0.1

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v4.0.0

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v3.9.2

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v3.9.1

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v3.9.0

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v3.8.4

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Configuration

📅 Schedule: At any time (no schedule defined).

🚦 Automerge: Disabled by config. Please merge this manually once you are satisfied.

♻ Rebasing: Whenever MR becomes conflicted, or you tick the rebase/retry checkbox.

🔕 Ignore: Close this MR and you won't be reminded about this update again.

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• If you want to rebase/retry this MR, click this checkbox.

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This MR has been generated by Renovate Bot.