dev_requirements file has incompatible requirements

[youcandanch]

Summary

When trying to install development requirements on a fresh repo, an error is thrown from pip. This is because we've upgraded the dev_requirements.txt file to include a dependency on pytest-flake8 1.1.1, but that library is only compatible with pytest 7 and above.

Environment details

• Windows 11, WSL2 running Debian GNU/Linux 11 (bullseye)
• Python version: 3.9.10
• pip version: 22.0.3

Steps to reproduce

1. Clone down the repository (or a fork) and check out the main branch (currently f545d4c)
2. Create a virtualenv. Python version shouldn't matter, but this is definitely reproducible on 3.9.
3. Try to install the dev requirements by doing pip install -r dev_requirements.txt.

Stack trace

INFO: pip is looking at multiple versions of pytest to determine which version is compatible with other requirements. This could take a while.
Collecting pytest==6.2.5
  Using cached pytest-6.2.5-py3-none-any.whl (280 kB)
INFO: pip is looking at multiple versions of <Python from Requires-Python> to determine which version is compatible with other requirements. This could take a while.
INFO: pip is looking at multiple versions of future to determine which version is compatible with other requirements. This could take a while.
Collecting future==0.18.2
  Using cached future-0.18.2-py3-none-any.whl
ERROR: Cannot install -r dev_requirements.txt (line 5) and pytest==6.2.5 because these package versions have conflicting dependencies.

The conflict is caused by:
    The user requested pytest==6.2.5
    pytest-flake8 1.1.1 depends on pytest>=7.0

To fix this you could try to:
1. loosen the range of package versions you've specified
2. remove package versions to allow pip attempt to solve the dependency conflict

ERROR: ResolutionImpossible: for help visit https://pip.pypa.io/en/latest/topics/dependency-resolution/#dealing-with-dependency-conflicts