[clang-tools-extra] [clang-tidy][NFC] Fix list.rst and add_new_check.py (PR #192228)

[Baranov Victor via cfe-commits]

vbvictor wrote:

> We should make it a lit test tbh, I would open another PR for it soon..

I'm very positive of tests that will check overall "wellbeing" of list and fail if existing heuristics produce a different output that current state of docs.

https://github.com/llvm/llvm-project/pull/192228