### Godot version

4.0.3.stable

### System information

Windows 10/11

### Issue description

I want the player's cursor to change when highlighting pickable Area2Ds; to do this, I have the areas modify the `mouse_default_cursor_shape` property on an external Control when the mouse enters or exits. If another Control appears in front of the Area2D while the mouse is over it, there is a chance that the project will crash.

Nothing prints to the IDE's output on this crash. If running the editor with console, then
```
ERROR: Condition "slot >= slot_max" is true. Returning: nullptr
   at: get_instance (./core/object/object.h:972)
```
will sometimes appear alongside the crash. If it appears, it always appears twice.

When I run a debug build of the editor through WinDbg, WinDbg will catch the following exception:
```
(3b58.2aac): Access violation - code c0000005 (!!! second chance !!!)
godot_windows_editor_x86_64!ObjectDB::get_instance [inlined in godot_windows_editor_x86_64!Viewport::_cleanup_mouseover_colliders+0x6f]:
00007ff6`ac254a1f 488b5310        mov     rdx,qword ptr [rbx+10h] ds:cccccccc`c31c419b=????????????????
```
When using this method, the exception is not random; it always occurs on the first attempt.

### Steps to reproduce

- Open the minimal reproduction project in the editor.
- Run the project.
- Click on the Area2D (you'll want visible collision shapes on).
- A full-screen button will pop up. If the game does not crash at this point, clicking the button will hide it so you can try again. It should crash within a few seconds of mashing.

### Minimal reproduction project

[Crash Test.zip](https://github.com/godotengine/godot/files/12027772/Crash.Test.zip)

ERR_READ_THREAD_GUARD_V(nullptr);
	return camera_2d;
}
Transform2D Viewport::get_final_transform() const {
	ERR_READ_THREAD_GUARD_V(Transform2D());
	return stretch_transform * global_canvas_transform;
}
void Viewport::assign_next_enabled_camera_2d(const StringName &p_camera_group) {
	ERR_MAIN_THREAD_GUARD;
	List<Node *> camera_list;
	get_tree()->get_nodes_in_group(p_camera_group, &camera_list);
	Camera2D *new_camera = nullptr;
	for (Node *E : camera_list) {
		Camera2D *cam = Object::cast_to<Camera2D>(E);
		if (!cam) {
			continue; 
		}
		if (cam->is_enabled()) {
			new_camera = cam;
			break;
		}
	}
	_camera_2d_set(new_camera);
	if (!camera_2d) {
		set_canvas_transform(Transform2D());
	}
}
void Viewport::_update_canvas_items(Node *p_node) {