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

---

Pull Request Etiquette

When creating PR:

• [ ] Make sure you're requesting to pull a branch (right side) to the develop branch (left side).
• [ ] Make sure you do not remove the "How to Review and Approve" section in your pull request description

After creating PR:

• [ ] Add yourself (and co-authors) as "Assignees" for PR.
• [ ] Add label to indicate if it's a Rule, Definition or Chore.
• [ ] Link the PR to any issue it solves. This will be done automatically by referencing the issue at the top of this comment in the indicated place.
• [ ] Optionally request feedback from anyone in particular by assigning them as "Reviewers".

When merging a PR:

• [ ] Close any issue that the PR resolves. This will happen automatically upon merging if the PR was correctly linked to the issue, e.g. by referencing the issue at the top of this comment.

How to Review And Approve

• Go to the “Files changed” tab
• Here you will have the option to leave comments on different lines.
• Once the review is completed, find the “Review changes” button in the top right, select “Approve” (if you are really confident in the rule) or "Request changes" and click “Submit review”.
• Make sure to also review the proposed Call for Review period. In case of disagreement, the longer period wins.