### Godot version

Master (4.2)

### System information

Windows 11 - Vulkan - Nvidia RTX 4070 - intel i5 13600KF

### Issue description

As you can see in the video when you try to add multiple scenes in to the 3D viewport (only with multiple scenes) the editor throws this error.

```
ERROR: Can't add child '@Node3D@18837' to '@SubViewport@9274', already has a parent '@SubViewport@9274'.
   at: (scene\main\node.cpp:1411)
```


Video: https://youtu.be/BVcCIigQJDw

This happens in the latest master (pulled on 2.11.2023).

### Steps to reproduce

Drag couple of the 3d mesh scenes into the 3D viewport and then select multiple scenes and drag them over and observer the error.

### Minimal reproduction project

[TestSceneDragAndDrop.zip](https://github.com/godotengine/godot/files/13253741/TestSceneDragAndDrop.zip)

ERR_FAIL_NULL(p_control);
	ERR_FAIL_COND(p_control->get_parent());
	VSeparator *sep = memnew(VSeparator);
	context_toolbar_hbox->add_child(sep);
	context_toolbar_hbox->add_child(p_control);
	context_toolbar_separators[p_control] = sep;
	p_control->connect("visibility_changed", callable_mp(this, &Node3DEditor::_update_context_toolbar));
	_update_context_toolbar();
}
void Node3DEditor::remove_control_from_menu_panel(Control *p_control) {
	ERR_FAIL_NULL(p_control);
	ERR_FAIL_COND(p_control->get_parent() != context_toolbar_hbox);
	p_control->disconnect("visibility_changed", callable_mp(this, &Node3DEditor::_update_context_toolbar));
	VSeparator *sep = context_toolbar_separators[p_control];
	context_toolbar_hbox->remove_child(sep);
	context_toolbar_hbox->remove_child(p_control);
	context_toolbar_separators.erase(p_control);
	memdelete(sep);
	_update_context_toolbar();
}
void Node3DEditor::_update_context_toolbar() {