Updated the Table of Contents block's block.json to remove declared non-support for customClassName. Support for customClassName is required for the Block Styles API.
How It Was Tested
[x] Local plugin dev environment
[x] Local theme dev environment with a registered style.
How To Test
[ ] Applying a custom CSS class to the table of contents block in the editor persists to the rendered content.
Related Issues
What Was Accomplished
How It Was Tested
How To Test