Shift-Tab (liftListItem) results in prosemirror invalid content error.

[iskaktoltay]

Describe the bug I have created a few paragraphs with nested children that look like this: Trying to shift tab on any second level nested child (test or test 3), except for the last one results in an invalid content error being thrown.

To Reproduce

1. Create a block.
2. Create a few nested child blocks (more than one).
3. Add another nested child block to all the child blocks created in step 2.
4. Click Shift + Tab on any second level nested block.

Misc Used the demo editor on your website.

Possible reason I believe the issue is with Tiptap's liftListItem command trying to insert the following child nodes into the content of blockContainer, while blockContainter can only have one content node and one blockGroup as its' children in your schema.