fix: Clarify 'No missing headings' summary text

[Modusensus (modusensus)]

Details

Clarifies the summary text for the "No missing headings" requirement (#7762). The previous wording ("Text that looks like a heading must be coded as a heading") can be confusing or misleading, since it can feed into the common misconception that headings should be used to format text. The new wording describes headings by their function instead of their appearance.

New wording:

Text that labels a section of the page must be coded as a heading.

This change touches:

• The requirement description in the headings assessment test step
• The "How to test" instructions for the same test step
• The associated guidance content page
• Test snapshots that mirror the updated text

Motivation

Addresses #7762

Pull request checklist

• Addresses an existing issue: Consider adjusting summary text for "5.2 No missing headings" #7762
• Ran yarn fastpass
• Added/updated relevant unit test(s) (and ran yarn test)
• Verified code coverage for the changes made
• PR title AND final merge commit title both start with a semantic tag (fix:, chore:, feat(feature-name):, refactor:). See CONTRIBUTING.md.
• (UI changes only) Added screenshots/GIFs to description above
• (UI changes only) Verified usability with NVDA/JAWS

[Modusensus (modusensus)]

@microsoft-github-policy-service agree