### Godot version

v4.0.beta.custom_build [0a9e6e478]

### System information

Ubuntu, Nvidia, Vulkan

### Issue description

When a Camera2D is freed - either explicitly or by being a child of a scene that is being switched away from via a method like `get_tree().change_scene_to_file()` - then this camera somehow stays active instead of Godot properly switching to no-camera-mode.

`get_viewport().get_camera_2d()` then returns all sorts of funny things from `<Freed Object>`  (it's supposed to return `null`) to arbitrary nodes of the current scene (not cameras).

This can lead to crashes.

### Steps to reproduce

checkout the MRP.

note that the "Go to scene 2" button switches places after pressing it.
that is because a camera is still active that does not exist in the current tree.

restart it a couple of times and spam the "Go to scene 2" button.
notice the garbage output.

### Minimal reproduction project

[godot_4_camera_bug.zip](https://github.com/godotengine/godot/files/10560455/godot_4_camera_bug.zip)
gui.roots.erase(RI);
}
void Viewport::_gui_unfocus_control(Control *p_control) {
	if (gui.key_focus == p_control) {
		gui.key_focus->release_focus();
	}
}
void Viewport::_gui_hide_control(Control *p_control) {
	if (gui.mouse_focus == p_control) {
		_drop_mouse_focus();
	}
	if (gui.key_focus == p_control) {
		gui_release_focus();
	}
	if (gui.mouse_over == p_control) {
		gui.mouse_over = nullptr;
	}
	if (gui.drag_mouse_over == p_control) {
		gui.drag_mouse_over = nullptr;
	}
	if (gui.tooltip_control == p_control) {
		_gui_cancel_tooltip();
	}
}
void Viewport::_gui_remove_control(Control *p_control) {