Update .gitignore

[wren]

This updates the .gitignore file to:

• Has the correct name for .tool-versions (per https://asdf-vm.com/manage/configuration.html#tool-versions)
• Adds the pytest cache directory (.pytest_cache per https://pytest.org/en/7.1.x/how-to/cache.html#inspecting-cache-content)
• Adds Python 3 bytcode directories (__pycache__ per https://docs.python.org/3/faq/programming.html?highlight=__pycache__#how-do-i-create-a-pyc-file)

Checklist

• I have read the contributing doc.
• I have included a link to the relevant issue number.
• I have checked to ensure there aren't other open pull requests
  for the same issue.
• I have written new tests for these changes, as needed.