Update flake8 requirement from <5,>=3.8.4 to >=3.8.4,<8

Updates the requirements on [flake8](https://github.com/pycqa/flake8) to permit the latest version.
- [Commits](PyCQA/flake8@3.8.4...7.0.0)

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

Signed-off-by: dependabot[bot] <support@github.com>

tests/requirements.txt

@@ -4,7 +4,7 @@ consolekit>=1.0.0
 coverage>=5.1
 coverage-pyver-pragma>=0.2.1
 faker>=4.1.2
-flake8<5,>=3.8.4
+flake8>=3.8.4,<8
 funcy>=1.16
 importlib-metadata>=3.6.0
 pandas>=1.0.0; implementation_name == "cpython" and python_version < "3.11"