Use alert callout in the block deprecation docs

[Mamaduka]

What?

PR updates block documentation docs to use alert callout in block deprecation docs to highlight an important caveat.

Why?

The fact that attributes|supports block settings aren't inherited by deprecation objects can be easily missed and result in broken deprecation. See #50281.

Testing Instructions

CI is green.

The callouts are rendered only on the docs page, so testing locally is hard.

[ndiego]

Looks good! 🚢

[github-actions]

Flaky tests detected in ba5386b.
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/4871489279
📝 Reported issues:

• [Flaky Test] should be disabled when post is being saved #35641 in specs/editor/various/publish-button.test.js