Bump @ckeditor/ckeditor5-widget in /examples/placeholder-demo

Bumps [@ckeditor/ckeditor5-widget](https://github.com/ckeditor/ckeditor5/tree/HEAD/packages/ckeditor5-widget) from 11.0.4 to 27.0.0.
- [Release notes](https://github.com/ckeditor/ckeditor5/releases)
- [Changelog](https://github.com/ckeditor/ckeditor5/blob/master/packages/ckeditor5-widget/CHANGELOG.md)
- [Commits](https://github.com/ckeditor/ckeditor5/commits/v27.0.0/packages/ckeditor5-widget)

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