### 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)
if (mb->get_device() == InputEvent::DEVICE_ID_TOUCH_MOUSE) {
					physics_has_last_mousepos = false;
				}
			}
		}
		Ref<InputEventKey> k = ev;
		if (k.is_valid()) {
			
			physics_last_mouse_state.alt = k->is_alt_pressed();
			physics_last_mouse_state.shift = k->is_shift_pressed();
			physics_last_mouse_state.control = k->is_ctrl_pressed();
			physics_last_mouse_state.meta = k->is_meta_pressed();
			continue;
		}
		Ref<InputEventScreenDrag> sd = ev;
		if (sd.is_valid()) {
			pos = sd->get_position();
		}
		Ref<InputEventScreenTouch> st = ev;
		if (st.is_valid()) {
			pos = st->get_position();
		}
		if (ss2d) {
			
			uint64_t frame = get_tree()->get_frame();
			PhysicsDirectSpaceState2D::ShapeResult res[64];
			for (const CanvasLayer *E : canvas_layers) {
				Transform2D canvas_layer_transform;
				ObjectID canvas_layer_id;
				if (E) {