`HtmlFormatter::nodeBegin` produces invalid HTML if Object-key contains unclosed HTML `<tag>`

Version: 3.0.6

Example:

```js
console.diff({'<script>': 0}, {a:1, b:2, d:3})
```

![Image](https://github.com/user-attachments/assets/3cd18302-1595-4da8-8d45-1b0a157b508f)