### 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)
return size;
}
void Viewport::set_disable_input(bool p_disable) {
	if (p_disable == disable_input) {
		return;
	}
	if (p_disable) {
		_drop_mouse_focus();
		_drop_mouse_over();
		_gui_cancel_tooltip();
	}
	disable_input = p_disable;
}
bool Viewport::is_input_disabled() const {
	return disable_input;
}
Variant Viewport::gui_get_drag_data() const {
	return gui.drag_data;
}
PackedStringArray Viewport::get_configuration_warnings() const {
	PackedStringArray warnings = Node::get_configuration_warnings();
	if (size.x <= 1 || size.y <= 1) {
		warnings.push_back(RTR("The Viewport size must be greater than or equal to 2 pixels on both dimensions to render anything."));
	}
	return warnings;
}
void Viewport::gui_reset_canvas_sort_index() {