[ally] notebook: fix arc toolkit issues

Created by: limitedmage

Closes #35670 (closed) Closes #35678 (closed) Closes #35681 (closed)

Test plan

• Verify checkmark icon is now hidden
• Verify notebook block is still tabbable and can navigate through blocks with arrow keys.
• Verify notebook blocks now have the correct role (article) using VoiceOver and that they are listed in the Landmarks menu.
• Verify ARC Toolkit no long shows errors about aria-label on divs (since div was changed to article for notebook blocks)

App preview:

• Web
• Storybook

Check out the client app preview documentation to learn more.