Document Outline: Headings in the template can be selected even though they are not editable

[carolinan]

Description

In the block editor, the Document Outline shows heading blocks that are part of the template if the option "show template" is enabled.

Each item in the Document Outline is a link that contains the client ID of the block.
When the link that represents a block in the template is activated, the block in the canvas is selected, even though it is not editable. The selected block is also missing a visible focus style.

It may be confusing for users that the block is selectable from the Document Outline when it can not be edited or removed.

Follow up to #69073

Step-by-step reproduction instructions

Activate Twenty Twenty-Five.
Clear any changes you may have made to the single page template.
Open or create a new page.
Enable the option "Show template".
Open the Document Outline panel.
In the list of blocks in the Document Outline, activate a link that belongs to a heading in the template, and observe what happens.

Screenshots, screen recording, code snippet

No response

Environment info

No response

Please confirm that you have searched existing issues in the repo.

• Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

• Yes

Please confirm which theme type you used for testing.

• Block
• Classic
• Hybrid (e.g. classic with theme.json)
• Not sure