### 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 (!is_inside_tree()) {
		return;
	}
	if (!physics_object_picking) {
		return;
	}
	if (to_screen_rect != Rect2i() && Input::get_singleton()->get_mouse_mode() == Input::MOUSE_MODE_CAPTURED) {
		return;
	}
	if (!gui.mouse_in_viewport) {
		
		physics_picking_events.clear();
		return;
	}
	_drop_physics_mouseover(true);
#ifndef _3D_DISABLED
	Vector2 last_pos(1e20, 1e20);
	CollisionObject3D *last_object = nullptr;
	ObjectID last_id;