bug(AMF Encode): Uncaught TypeError setting getter-only property "value"

To reproduce that, drag AMF Encode and set the input simply to `{"a": true}`
as you can see an unhandled TypeError appear thrown as that

```js
AMF Encode - TypeError in https://gchq.github.io/CyberChef/modules/Encodings.js on line 2.

Message: setting getter-only property "value"
```

Direct Test Links:
- https://gchq.github.io/CyberChef/#recipe=AMF_Encode('AMF3')&input=eyJhIjogdHJ1ZX0&oenc=65001&oeol=VT
- https://gchq.github.io/CyberChef/#recipe=AMF_Encode('AMF3')&input=eyJhIjogbnVsbH0&oenc=65001&oeol=VT
- https://gchq.github.io/CyberChef/#recipe=AMF_Encode('AMF3')&input=eyJhIjogZmFsc2V9&oenc=65001&oeol=VT

Reproduce the error with the AMF Encode recipe using the linked inputs, then inspect modules/Encodings.js around the AMF Encode implementation. Done means encoding inputs containing true, null, and false no longer throws the reported TypeError.

Written by the indexing model from the issue text.