### Godot version

4.1.dev4

### System information

Windows 10 - Godot 4.1.dev4 - Compatibility

### Issue description

When you syncronize 2 variables and both are in watched mode (taking out the "sync" property too) the server crashes

### Steps to reproduce

Create a MultiplayerSynchronizer, export 2 variables from a script, connect the server and the client and the server will crash instantly

In the project I give, the server and client are connected automatically when you use 2 debug instances when pressing play

### Minimal reproduction project

[minimalproject.zip](https://github.com/godotengine/godot/files/11665652/minimalproject.zip)

Node *node = Object::cast_to<Node>(p_obj);
	ERR_FAIL_COND_V(!node || p_config.get_type() != Variant::OBJECT, ERR_INVALID_PARAMETER);
	MultiplayerSpawner *spawner = Object::cast_to<MultiplayerSpawner>(p_config.get_validated_object());
	ERR_FAIL_COND_V(!p_obj || !spawner, ERR_INVALID_PARAMETER);
	
	int len = 0;
	Error err = _make_despawn_packet(node, len);
	ERR_FAIL_COND_V(err != OK, ERR_BUG);
	const ObjectID oid = p_obj->get_instance_id();
	for (const KeyValue<int, PeerInfo> &E : peers_info) {
		if (!E.value.spawn_nodes.has(oid)) {
			continue;
		}
		_send_raw(packet_cache.ptr(), len, E.key, true);
	}
	
	ERR_FAIL_COND_V(!tracked_nodes.has(oid), ERR_INVALID_PARAMETER);
	TrackedNode &tobj = _track(oid);
	ERR_FAIL_COND_V(tobj.spawner != spawner->get_instance_id(), ERR_INVALID_PARAMETER);
	tobj.spawner = ObjectID();
	spawned_nodes.erase(oid);
	for (KeyValue<int, PeerInfo> &E : peers_info) {
		E.value.spawn_nodes.erase(oid);
	}
	return OK;
}
Error SceneReplicationInterface::on_replication_start(Object *p_obj, Variant p_config) {