Bug: Multiline list items have all but first line deleted on backspace next to checkbox.

Lexical version:
0.11.3 - reproducible in playground

## Steps To Reproduce

1. Copy some text with newlines (e.i. "shift + enter) into the clipboard
2. Create a checkbox and indent it
3. Paste from the clipboard into the indented checkbox line
4. Hit backspace at the start of the checkbox line

Link to code example: https://playground.lexical.dev/

## The current behavior
All lines after the first line in the multiline list item will be deleted

## The expected behavior
The checkbox will either outdent or be deleted