### 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)
local_input_handled = false;
	Ref<InputEvent> ev;
	if (!p_local_coords) {
		ev = _make_input_local(p_event);
	} else {
		ev = p_event;
	}
	Ref<InputEventMouse> me = ev;
	if (me.is_valid()) {
		gui.last_mouse_pos = me->get_position();
	}
	if (is_embedding_subwindows() && _sub_windows_forward_input(ev)) {
		set_input_as_handled();
		return;
	}
	if (!_can_consume_input_events()) {
		return;
	}
	if (!is_input_handled()) {
		get_tree()->_call_input_pause(input_group, SceneTree::CALL_INPUT_TYPE_INPUT, ev, this); 
	}
	if (!is_input_handled()) {
		_gui_input_event(ev);
	} else {
		
		_gui_cleanup_internal_state(ev);
	}
	event_count++;
}
void Viewport::push_unhandled_input(const Ref<InputEvent> &p_event, bool p_local_coords) {