### 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);
	if (singleton->full_gdscript_cache.has(p_path)) {
		return singleton->full_gdscript_cache[p_path];
	}
	if (singleton->shallow_gdscript_cache.has(p_path)) {
		return singleton->shallow_gdscript_cache[p_path];
	}
	return Ref<GDScript>();
}
Error GDScriptCache::finish_compiling(const String &p_owner) {