Navigation Block: Submenu additional class duplication

[jacobcassidy]

Description

When adding a class to a submenu block under "Advanced", it gets duplicated in the HTML twice. If you add multiple classes, they all get duplicated twice.

Step-by-step reproduction instructions

1. In the Editor, add a submenu block
2. Add a class for the submenu block in Advanced > Additional CSS class(es)
3. Save your page
4. Go to the live page and inspect the submenu block
5. Notice the additional class(es) you added are inserted twice.

Screenshots, screen recording, code snippet

Add class called test-submenu

Check live page HTML for duplication of class:

Environment info

• WP v5.8.2
• Glutenberg v11.9.0
• Chrome v95
• macOS

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

[talldan]

Looks like this should be a pretty simple fix. It has already been fixed in the navigation link block in #35634 by deleting some code.

It should be possible to do the same in the submenu block.