Add `Tools/check-c-api-docs` to mypy check

[sobolevn]

Feature or enhancement

It is already typed: https://github.com/python/cpython/blob/8307a14d0edc14ae2f775995720e4b6d6dc865b3/Tools/check-c-api-docs/main.py

We only need a mypy.ini file like we do in https://github.com/python/cpython/blob/8307a14d0edc14ae2f775995720e4b6d6dc865b3/.github/workflows/mypy.yml

Linked PRs

• gh-142859: Add Tools/check-c-api-docs to mypy check #142860
• [3.13] gh-142859: Add Tools/check-c-api-docs to mypy check (GH-142860) #142870
• [3.14] gh-142859: Add Tools/check-c-api-docs to mypy check (GH-142860) #142871