Update flake8 requirement from ^3.8 to ^5.0 (#33)

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@3.8.0...5.0.2)

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

Signed-off-by: dependabot[bot] <[email protected]>

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

pyproject.toml

@@ -25,7 +25,7 @@ django = "^2.2||^3.0||^4.0"
 [tool.poetry.dev-dependencies]
 bump2version = "^1.0"
 mock = "^4.0"
-flake8 = "^3.8"
+flake8 = "^5.0"
 pytest = "^7.0"
 pytest-cov = "^4.0"
 pytest-django = "^4.5"