Final call: text-contrast: make passed example 7 a failed example

Hey folks,
After some discussion in the ACT TF, I've concluded I was incorrect about
one of the examples. Passed example 7 is actually a failure of WCAG. To
capture this (and prevent this from coming up again), I'm changing this
example to a failed example instead. This final call ends on September
22nd. If you have any concerns, please leave a review:

https://github.com/act-rules/act-rules.github.io/pull/1435

Kind regards,

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