ci: Don't include API/what's new notes in general doc labels

[QuLogic]

PR summary

PRs that touch doc/users/next_whats_new/* because they have a new feature shouldn't be labelled as "user guide" updates, and similar for API notes.

PR checklist

• [n/a] "closes #0000" is in the body of the PR description to link the related issue
• [n/a] new and changed code is tested
• [n/a] Plotting related features are demonstrated in an example
• [n/a] New Features and API Changes are noted with a directive and release note
• [n/a] Documentation complies with general and docstring guidelines

[timhoffm]

We don't have an explicit guideline for infrastructure at https://matplotlib.org/devdocs/devel/pr_guide.html#merging. But I think such changes can be merged with just one approval.

[timhoffm]

Ping @QuLogic

This appears to not work. It caused a failure in #27690:

[QuLogic]

Oops, I deleted a -to- somehow. I wonder if I can find a schema somewhere so I can lint these before hand.