### Godot version

4.1.beta.a83eb16fb

### System information

Arch Linux

### Issue description

When attempting to have a scene load a resource that uses a script that exports a var of Callable type, a parse error will occur due to Callable not being serializable.

### Steps to reproduce

Create new project.
create a resource script that exports a Callable type:

```
class_name BreakStuff
extends Resource
@export var something: Callable
```

create a .tres file that uses the script.

create a scene that uses that resource, such as with a script like

```
extends Node
@export var stuff: Resource
```

set that resource to that .tres file.

close project and reopen.

Be greeted with error message about a parse error and be unable to open that scene.

Within plain text of .tscn file you can see a line that reads
something =

which causes a parse error as something has nothing to be set to.



### Minimal reproduction project

N/A
ERR_FAIL_COND_V_MSG(spawn_limit && spawn_limit <= tracked_nodes.size(), nullptr, "Spawn limit reached!");
	ERR_FAIL_COND_V_MSG(!spawn_function.is_valid(), nullptr, "Custom spawn requires a valid 'spawn_function'.");
	const Variant *argv[1] = { &p_data };
	Variant ret;
	Callable::CallError ce;
	spawn_function.callp(argv, 1, ret, ce);
	ERR_FAIL_COND_V_MSG(ce.error != Callable::CallError::CALL_OK, nullptr, "Failed to call spawn function.");
	ERR_FAIL_COND_V_MSG(ret.get_type() != Variant::OBJECT, nullptr, "The spawn function must return a Node.");
	return Object::cast_to<Node>(ret.operator Object *());
}
Node *MultiplayerSpawner::spawn(const Variant &p_data) {
	ERR_FAIL_COND_V(!is_inside_tree() || !get_multiplayer()->has_multiplayer_peer() || !is_multiplayer_authority(), nullptr);
	ERR_FAIL_COND_V_MSG(spawn_limit && spawn_limit <= tracked_nodes.size(), nullptr, "Spawn limit reached!");
	ERR_FAIL_COND_V_MSG(!spawn_function.is_valid(), nullptr, "Custom spawn requires the 'spawn_function' property to be a valid callable.");
	Node *parent = get_spawn_node();
	ERR_FAIL_COND_V_MSG(!parent, nullptr, "Cannot find spawn node.");
	Node *node = instantiate_custom(p_data);
	ERR_FAIL_COND_V_MSG(!node, nullptr, "The 'spawn_function' callable must return a valid node.");
	_track(node, p_data);
	parent->add_child(node, true);
	return node;
}