Markdown task list checkboxes render incorrectly in preview

Does this issue occur when all extensions are disabled?: Yes

- VS Code Version: 1.134.0
- OS Version: 110a328ea54b42367b803ec53ee0bf52ef26b419

## Issue

Markdown task lists (`- [ ]` / `- [x]`) are not rendered correctly in the Markdown preview. The checkboxes appear as incorrect squares instead of proper task-list checkboxes.

### Steps to Reproduce

```md
- [x] Review the code changes
- [ ] Update the documentation
- [ ] Deploy to production
```

Open the Markdown preview.

### Expected

Checked and unchecked items should render as standard Markdown task-list checkboxes.