Block JSON schema: add visibility key to supports definition

[shimotmk]

What?

Related #57373

This PR adds visibility key to supports definition in block.json schema.

Why?

How?

Testing Instructions

You should see the visibility key listed in the supports property.

[github-actions]

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Co-authored-by: shimotmk <shimotomoki@git.wordpress.org>
Co-authored-by: t-hamano <wildworks@git.wordpress.org>

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[t-hamano]

Nice catch!

Can you add the visibility section to the end of this file following the format of the other sections?

[shimotmk]

@t-hamano
Thank you! I fixed it

[t-hamano]

LGTM!

[github-actions]

Flaky tests detected in d8e276f.
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/19734122611
📝 Reported issues:

• [Flaky Test] should show the original content after revert, clicking undo then redo in the header toolbar #47896 in /test/e2e/specs/site-editor/template-revert.spec.js

[t-hamano]

This PR has been backported to the wp/6.9 branch. #74806