Skip writing pyc files [ci]

[cdce8p]

Proposed change

Skip writing bytecode files for pytest runs - a small performance improvement. This is only really important for pytest as it compiles all test files as well. The other linters just read them as text files.
https://docs.python.org/3/using/cmdline.html#envvar-PYTHONDONTWRITEBYTECODE
https://docs.pytest.org/en/7.1.x/how-to/assert.html#assertion-rewriting-caches-files-on-disk

I also explored caching those to speed up pytest even more. However the .pyc files are regenerated based on the mtime of the source code which resets with each git checkout. Thus, caching them unfortunately doesn't really work.

Update
Reading on it some more, Python does actually support hash based .pyc checks via the --invalidation-mode option.
https://docs.python.org/3/reference/import.html#cached-bytecode-invalidation
https://docs.python.org/3/library/compileall.html#cmdoption-compileall-invalidation-mode

However, pytest certainly does not.
https://github.com/pytest-dev/pytest/blob/7.4.0/src/_pytest/assertion/rewrite.py#L387-L390

Even if it would, there is still the issue that the test suite is split into multiple groups. Therefore the bytecode files would likely need to be combined for caching to be effective. A lot of work. I might explore it in the future but for now simply disabling writing the bytecode files provides the most improvements.

Type of change

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[frenck]

Thanks, @cdce8p 👍

../Frenck