Call for review: Heading descriptive: Fix some of the examples

Hey folks,

This pull request fixes a typo in one of the "Heading is descriptive" rule,
and tweaks some of its examples to make these examples a bit easier to
understand. If you have any comments, please leave a review by May 5th:
https://github.com/act-rules/act-rules.github.io/pull/1827

Kind regards

-- 
*Wilco Fiers*
Axe-core & Axe-linter product owner - WCAG 3 Project Manager - Facilitator
ACT Task Force