Update style checks instructions in the Contributing Guide

[santisoler]

We should update the instructions on checking the code style of our packages in the CONTRIBUTING.md. Currently, it informs the contributors that we use flake8 and pylint to lint our code, and to run make lint to run pylint only.

We are not using pylint anymore in most of our packages, so would be nice to update those instructions to remove it.

If we finally implement ruff for linting and auto-formatting, we should mention it as well, but this could be a separate issue/PR.