### 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)

if (spawn_queue.size()) {
		ERR_PRINT("An error happened during last spawn, this usually means the 'ready' signal was not emitted by the spawned node.");
		for (const ObjectID &oid : spawn_queue) {
			Node *node = get_id_as<Node>(oid);
			ERR_CONTINUE(!node);
			if (node->is_connected(SceneStringNames::get_singleton()->ready, callable_mp(this, &SceneReplicationInterface::_node_ready))) {
				node->disconnect(SceneStringNames::get_singleton()->ready, callable_mp(this, &SceneReplicationInterface::_node_ready));
			}
		}
		spawn_queue.clear();
	}
	
	uint64_t usec = OS::get_singleton()->get_ticks_usec();
	for (KeyValue<int, PeerInfo> &E : peers_info) {
		const HashSet<ObjectID> to_sync = E.value.sync_nodes;
		if (to_sync.is_empty()) {
			continue; 
		}
		uint16_t sync_net_time = ++E.value.last_sent_sync;
		_send_sync(E.key, to_sync, sync_net_time, usec);
		_send_delta(E.key, to_sync, usec, E.value.last_watch_usecs);
	}
}
Error SceneReplicationInterface::on_spawn(Object *p_obj, Variant p_config) {