### 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
MutexLock lock(singleton->mutex);
	Ref<GDScriptParserRef> ref;
	if (!p_owner.is_empty()) {
		singleton->dependencies[p_owner].insert(p_path);
	}
	if (singleton->parser_map.has(p_path)) {
		ref = Ref<GDScriptParserRef>(singleton->parser_map[p_path]);
		if (ref.is_null()) {
			r_error = ERR_INVALID_DATA;
			return ref;
		}
	} else {
		if (!FileAccess::exists(p_path)) {
			r_error = ERR_FILE_NOT_FOUND;
			return ref;
		}
		GDScriptParser *parser = memnew(GDScriptParser);
		ref.instantiate();
		ref->parser = parser;
		ref->path = p_path;
		singleton->parser_map[p_path] = ref.ptr();
	}
	r_error = ref->raise_status(p_status);
	return ref;
}
String GDScriptCache::get_source_code(const String &p_path) {