Re:#118694 (comment)

We have tooling in place to ensure reST files underDoc/ don't introduce new Sphinx reference warnings.

We ignore those that are in.nitignore because they've not been "cleaned" yet, because we don't want to hassle people over warnings which they didn't introduce.

Similarly, we ignore the news files underMisc/NEWS.d/, because during the Sphinx build,blurb compiles then into a giant 45k linebuild/NEWS which has 700+ warnings (and growing, because we don't check them).

We do lint the news files with Sphinx Lint, but that doesn't catch everything, especially not bad references.

And so we don't want to warn for every single PR that adds a small NEWS blurb about those 700 warnings that they didn't introduce.

New entries are added to the top of the compiled NEWS file.

This PR adds a check to ensure the top 200 lines remain clean. Most NEWS entries are under 10 lines long, and the biggest right now is 18 lines, so checking the top 200 will prevent new warnings being introduced.

I cleaned the top 200 lines (3 news files), but also introduced one temporarily to demonstrate how the CI fails. I'll revert that commit before merge.

📚 Documentation preview 📚:https://cpython-previews--119221.org.readthedocs.build/