Final call: Add required aria-checked attribute to ARIA required owns passed example 4

Hey folks,
Small pull request improving the examples of the ARIA required owned
elements rule. This final call ends on August 21st. If you have any
feedback, please leave a review before that date:

https://github.com/act-rules/act-rules.github.io/pull/1414

-- 
*Wilco Fiers*
Axe for Web product owner - Co-facilitator WCAG-ACT - Chair ACT-R