### 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)

String name;
	switch (view_type) {
		case VIEW_TYPE_USER: {
			if (orthogonal) {
				name = TTR("Orthogonal");
			} else {
				name = TTR("Perspective");
			}
		} break;
		case VIEW_TYPE_TOP: {
			if (orthogonal) {
				name = TTR("Top Orthogonal");
			} else {
				name = TTR("Top Perspective");
			}
		} break;
		case VIEW_TYPE_BOTTOM: {
			if (orthogonal) {
				name = TTR("Bottom Orthogonal");
			} else {
				name = TTR("Bottom Perspective");
			}
		} break;
		case VIEW_TYPE_LEFT: {
			if (orthogonal) {
				name = TTR("Left Orthogonal");
			} else {
				name = TTR("Left Perspective");
			}
		} break;