Update C43 to add test case for Focus Not Obscured Enhanced

[fstrr]

Closes #3532

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[bruce-usab]

Discussed on backlog call 9/6.

[detlevhfischer]

Why is it that the Deploy Preview links always seem to be broken? Having a link to a clean preview would simplify the review.

[patrickhlauke]

@detlevhfischer the deploy links need to be manually expanded to include the actual file you're trying to look at (the deploy preview has no root/index). so in this case, the deploy preview is https://deploy-preview-3534--wcag2.netlify.app/, the file changed here is techniques/css/C43.html, so you want to manually go to https://deploy-preview-3534--wcag2.netlify.app/techniques/css/c43

(with hat tip to @kfranqueiro for pointing that out to me recently)

It would of course be super helpful if the deploy preview had some form of initial index (even if just a throwaway page that points to /techniques/ and /understanding/