[Call for review] Tweaks to expectations to "Block of repeated content is collapsible"

This PR tries to clarify the expectations and background sections for the rule "Block of repeated content is collapsible".
https://github.com/act-rules/act-rules.github.io/pull/1802


This PR requires a 1-week call for review.

Best.

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Daniel Montalvo

Accessibility Education and Training Specialist
W3C/WAI