Empty contextual block control toolbar rendering when in content view

[richtabor]

Description

It's a tiny empty block toolbar that is consistently showing up when selecting blocks in the content-only view of pages within the Site Editor.

Step-by-step reproduction instructions

1. View a page from within the Site Editor > Pages panel.
2. Click on editable blocks.
3. See an empty toolbar.

Screenshots, screen recording, code snippet

Environment info

Gutenberg trunk

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