Fix: Revision REST schema remove protected

[DarkMatter-999]

Trac ticket: https://core.trac.wordpress.org/ticket/53417

The schema provided by the REST API endpoints for revisions at wp/v2/posts/{id}/revisions and wp/v2/pages/{id}/revisions incorrectly states that content.protected and excerpt.protected properties exist. Revisions do not inherently support password protection in their response payloads, as they belong to the parent post.

This PR fixes the issue by removing the protected property from the revision schema for both the content and excerpt fields within WP_REST_Revisions_Controller::get_item_schema().

Use of AI Tools

AI assistance: Yes
Tool(s): Github Copilot (Claude 4.6 Sonnet, Gemini 3.1 Pro)
Used for: Discussing the implementation approach and refining the PHPUnit tests for schema validation. Final code and tests were reviewed and verified locally by me.

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