Update dependencies and tooling

[klane]

• Fixes CI pipelines that were broken due to the deprecated set-output command
• Drops support for Python 3.6-3.8
• Updates dependencies, pre-commit hooks and GitHub Actions
• Adds mkdocs as a dev dependency to build documentation locally
• Adds pytest-xdist as a dev dependency to run tests in parallel
• Removes pytest-lazy-fixture as a dev dependency since it does not support pytest 8
• Removes tox as a dev dependency
• Migrates code formatting and linting to ruff