Update flake8 requirement from ^4.0.1 to ^5.0.4 (#48)

Updates the requirements on [flake8](https://github.com/pycqa/flake8) to permit the latest version.
- [Release notes](https://github.com/pycqa/flake8/releases)
- [Commits](PyCQA/flake8@4.0.1...5.0.4)

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

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pyproject.toml

@@ -24,7 +24,7 @@ pytest-cov = "^3.0.0"
 black = "^22.1"
 isort = "^5.9.3"
 mypy = "^0.971"
-flake8 = "^4.0.1"
+flake8 = "^5.0.4"
 pytest = "^7.0.0"
 nox = "^2022.1.7"