Run flake8 without an env on Github CI

[inducer]

In a way, this addresses
zheller/flake8-quotes#117, since it forces the Python that runs flake8 onto 'oldest supported', currently 3.8.

[alexfikl]

Why was this picking up python 3.12? The CI already sets python-version: '3.8' in the flake8 job for compatibility..

[inducer]

That 3.8 specified the Python version installed by Github, which was shortly thereafter made moot by the conda env being installed.

[alexfikl]

Hmm, that's a bit confusing.. Should we do a conda env create python=$PYTHON_VERSION or something like that in ci-support?

Only pytools seems to be doing a matrix on the python-version and it uses venv directly, so that works. Most other projects try to run flake8 on python-version: '3.8' with conda and probably have the same issue as this, but it didn't complain yet..

[inducer]

IDK. Kind of reluctant to attempt to overengineer something here.