BlockToolbar: Disabling group block variations is not applied

[t-hamano]

Description

Related: #39710

In #39710, group block variation buttons are displayed on the block toolbar when multiple blocks are selected.
However, they are still retained even when the variation is disabled by unregisterBlockVariation.

Step-by-step reproduction instructions

• Execute the following code from the browser console to disable the group block variation:

wp.blocks.unregisterBlockVariation('core/group', 'group-row');
wp.blocks.unregisterBlockVariation('core/group', 'group-stack');

• Add multiple blocks and select them.
• Confirm that the group block variation remains on the block toolbar.

Screenshots, screen recording, code snippet

6eec8b9c010c185c1dfac97ea66c3eb0.mp4

Environment info

• WordPress Version: 6.0-RC3
• Gutenberg Version: 13.2.2
• Theme: Twenty Twenty Two

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