Fixes regression in Portable Text

• Fixes a regression introduced in v3.64.1 that caused Portable Text content to be hidden when part of a read-only document.

To initiate a new Sanity Studio project or upgrade an existing one, please refer to our comprehensive guide on Installing and Upgrading Sanity Studio.

If you are updating from a version earlier than 3.37.0, you should also check out this article to ensure your dependencies are up to date.