OS.execute cannot capture shell output

executing applications works fine like xterm for example or firefox
but i cannot get the shell output from command line apps like ls

```ts
_ready() {
let args = new godot.PoolStringArray(["-c", "ls"])
let arr = []
godot.OS.execute("sh", args, true, arr)

godot.print(arr) // prints empty []
}
```

Start at the OS.execute entry point shown in the TypeScript example and reproduce `sh -c ls` from `_ready()`, checking how the output array is populated. Done means command-line output is available through `arr` rather than producing an empty array.

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