Source Editing is not working in Inline Editor

[woaiiimipi]

📝 Provide detailed reproduction steps (if any)

1. Open ckeditor online build: https://ckeditor.com/ckeditor-5/online-builder/
2. Select Inline Editor
3. Select Source Editing function
4. Add Source Editing to toolbar
5. Open sample/index.html
6. Click Source Editing button, there is no response

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