Can't change parent of a node that has MultiplayerSpawners embedded. Server crashes.

### Tested versions

4.3.beta1

### System information

Windows 11 - Godot 4.3.beta1 - Forward+

### Issue description

Hello there, Sorry if I am reporting too many bugs for multiplayer issues. If I'm mistaken in what I've seen so far please let me know, but I haven't found a way to get to this specific goal, which is, to have a synchronized Entity through MultiplayerSpawners, and also have that Entity synchronize some of its children through MultiplayerSpawners too.

Thank you for your patience!

### Steps to reproduce

1. Make a main scene and add 2 nodes A and B as siblings to it. Each of them will synchronize the same scene through MultiplayerSpawners.
2. Create the empty Node scene D.
3. Create the scene C with a MultiplayerSpawner node that synchronizes the child scene D.
4. Run the game.
5. Connect server and client.
6. Instantiate C in A on the server, there is no need to instantiate the children.
7. Try to A.remove_child(C) and then B.add_child(C)
8. Server crashes

### Minimal reproduction project (MRP)

[minimal-project.zip](https://github.com/user-attachments/files/15910876/minimal-project.zip)

Start by running the attached minimal-project.zip with the stated Godot 4.3.beta1 setup and follow the eight reproduction steps, especially moving C from A to B on the server. Trace the MultiplayerSpawner and node-parenting path that handles this move. Done means the server no longer crashes and the synchronized entity remains functional after reparenting.

Written by the indexing model from the issue text.