docs: update blocks example to remove deprecated TinaTemplate type

[Klrfl]

General Contributing:

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

All New Content Submissions: (To be confirmed by reviewer)

• Title is short & specific
• Headers are logically ordered & consistent
• Purpose of document is explained in the first paragraph
• Procedures are tested and work
• Any technical concepts are explained or linked to
• Document follows structure from templates
• All links work
• The spelling and grammar checker has been run
• Graphics and images are clear and useful
• Any prerequisites and next steps are defined.

[vercel]

@Klrfl is attempting to deploy a commit to the TinaCMS Team on Vercel.

A member of the Team first needs to authorize it.

[wicksipedia]

Closing this as we won't be able to preview a build from a fork.

Re-opened as #2280
Commits have been cherry picked to retain attribution.