test: check stability block position in API markdown

[Renegade334]

The doc generator will only add a stability marker to the index if the blockquote element appears close to the relevant heading. There is an ordering convention (<heading> [<yaml>] <stability>) which is not currently enforced.

Adding a test for this identifies one element which is currently non-compliant, buf.slice() in buffer.md, which does not appear as deprecated in the index due to the malpositioned deprecation block.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.72%. Comparing base (65df9ad) to head (f523724).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #58590      +/-   ##
==========================================
- Coverage   89.73%   89.72%   -0.01%     
==========================================
  Files         675      675              
  Lines      204797   204797              
  Branches    39342    39348       +6     
==========================================
- Hits       183767   183764       -3     
- Misses      13294    13299       +5     
+ Partials     7736     7734       -2     

see 26 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[Renegade334]

Rebased as an additional failure case was introduced since the original commit.

[gurgunday]

lgtm

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/71344/

[nodejs-github-bot]

Landed in 9cc7fcc