What?

I noticed that because the class name prop is hard-coded, the block editor is not applying the proper CSS classes, and I couldn’t even select the block itself. This issue only occurs when the form block is nested. I don't know why it worked fine at the root level, but it was probably just a coincidence.

How?

Remove the hard-coded classname.

Note: This PR is effectively a part of #55755, and the issues occurring on the frontend need to be fixed separately.

Testing Instructions

• Insert a Form Block.
• Wrap the block with a Group block.
• Open the list view.
• Click the "Experimental Comment Form" row.
• Make sure you can select the block and that the block sidebar is visible.
• Click a block inside the Form block.
• Click the Parent Block Selection button on the left of the block toolbar.
• Make sure the Form block is selected.

Screenshots or screencast

The following screencast shows the issue occurring in the trunk branch: