### Godot version

4.1.dev

### System information

Win11

### Issue description

I load a non-existing GDScript, but it still returns a valid instance instead of null.
```gdscript
@tool
extends EditorScript

func _run():
	var s = ResourceLoader.load("non_exists.gd", "", ResourceLoader.CACHE_MODE_IGNORE)
	print(s)
	assert(s == null)

```

```
  Attempt to open script 'res://non_exists.gd' resulted in error 'File not found'.
<GDScript#-9223369015982753437>
  res://new_script.gd:7 - Assertion failed.

```

### Steps to reproduce

N/A

### Minimal reproduction project

N/A
if (r_error) {
		*r_error = ERR_FILE_CANT_OPEN;
	}
	Error err;
	Ref<GDScript> scr = GDScriptCache::get_full_script(p_path, err, "", p_cache_mode == CACHE_MODE_IGNORE);
	if (scr.is_null()) {
		
		scr.instantiate();
	}
	if (r_error) {
		*r_error = OK;
	}
	return scr;
}
void ResourceFormatLoaderGDScript::get_recognized_extensions(List<String> *p_extensions) const {