Cover block: disable contrast checker

[ramonjd]

What?

Resolves #50531

Let's deactivate the contrast checker on the cover block!

Why?

Given the combination of text, image, alpha and overlay color, it's just too much for the contrast checking algorithm to cope.

See discussion on the current issue or a past PR.

How?

Whacking "enableContrastChecker": false in the Cover block's block.json.
Too easy.

Testing Instructions

1. Insert a Cover block into a post
2. Set the same color for overlay and text
3. Witness that the contrast checker does not come to the party

Example HTML (you'll have to replace the image)

<!-- wp:cover {"url":"http://localhost:8888/wp-content/uploads/2023/07/Eq_it-na_pizza-margherita_sep2005_sml.jpg.webp","id":7,"dimRatio":50,"customOverlayColor":"#f2f0f0","isDark":false,"style":{"elements":{"link":{"color":{"text":"#f7f2f2"}}},"color":{"text":"#f7f2f2"}},"layout":{"type":"constrained"}} -->
<div class="wp-block-cover is-light has-text-color has-link-color" style="color:#f7f2f2"><span aria-hidden="true" class="wp-block-cover__background has-background-dim" style="background-color:#f2f0f0"></span><img class="wp-block-cover__image-background wp-image-7" alt="" src="http://localhost:8888/wp-content/uploads/2023/07/Eq_it-na_pizza-margherita_sep2005_sml.jpg.webp" data-object-fit="cover"/><div class="wp-block-cover__inner-container"><!-- wp:paragraph {"align":"center","placeholder":"Write title…","fontSize":"large"} -->
<p class="has-text-align-center has-large-font-size">A sweet cover block</p>
<!-- /wp:paragraph --></div></div>
<!-- /wp:cover -->

Screenshots or screencast

Before	After

[github-actions]

Flaky tests detected in 2ec77b4.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/5686445315
📝 Reported issues:

• [Flaky Test] Pick the additional variation in the inserted Columns block #47057 in specs/editor/plugins/block-variations.test.js

[ndiego]

Works like a charm. LGTM 🚀