Added text-shadow failure - Text has minimum contrast [afw4f7]

[giacomo-petri]

Closes: #2172

Often, there's a misunderstanding that including a text-shadow property automatically ensures that text will have a satisfactory contrast ratio with its background.
To dispel this notion, I've provided an example where the text-shadow property fails to guarantee adequate contrast, contrasting with the Passed Example 4, to emphasize that relying solely on text-shadow doesn't always ensure sufficient contrast.

Need for Call for Review:
This will require a 2 weeks Call for Review

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[WilcoFiers]

Talked this over with Carlos earlier this week. I think a better example here would be one that shows text-shadow actually creating a failure, rather than one where text-shadow can be ignored.

[giacomo-petri]

2 weeks call for review ends on August 16th.