### 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)
physics_picking_events.pop_front();
		Vector2 pos;
		bool is_mouse = false;
		Ref<InputEventMouseMotion> mm = ev;
		if (mm.is_valid()) {
			pos = mm->get_position();
			is_mouse = true;
			physics_has_last_mousepos = true;
			physics_last_mousepos = pos;
			physics_last_mouse_state.alt = mm->is_alt_pressed();
			physics_last_mouse_state.shift = mm->is_shift_pressed();
			physics_last_mouse_state.control = mm->is_ctrl_pressed();
			physics_last_mouse_state.meta = mm->is_meta_pressed();
			physics_last_mouse_state.mouse_mask = mm->get_button_mask();
		}
		Ref<InputEventMouseButton> mb = ev;
		if (mb.is_valid()) {
			pos = mb->get_position();
			is_mouse = true;
			physics_has_last_mousepos = true;
			physics_last_mousepos = pos;
			physics_last_mouse_state.alt = mb->is_alt_pressed();
			physics_last_mouse_state.shift = mb->is_shift_pressed();
			physics_last_mouse_state.control = mb->is_ctrl_pressed();
			physics_last_mouse_state.meta = mb->is_meta_pressed();
			if (mb->is_pressed()) {
				physics_last_mouse_state.mouse_mask.set_flag(mouse_button_to_mask(mb->get_button_index()));
			} else {
				physics_last_mouse_state.mouse_mask.clear_flag(mouse_button_to_mask(mb->get_button_index()));