libcst.tool: add support Python 3.9, 3.10, 3.11, 3.12 and 3.13

[jorenham]

Currently, running e.g. libcst.tool codemod --python-version=3.9 ... will raise a ValueError with the message:

ValueError: LibCST can only parse code using one of the following versions of Python's grammar: 3.0, 3.1, 3.3, 3.5, 3.6, 3.7, 3.8. More versions may be supported by future releases.

This adds the missing supported python version strings.

[zsol]

Unfortunately that flag doesn't actually do anything anymore by default¹, so I'd rather remove it.

Footnotes

1. It only controls the behavior of the old, unmaintained pure python parser which you can enable with an environment variable. That parser doesn't support 3.9 or newer. ↩