### 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 (gui.dragging) {
			
			Control *drag_preview = _gui_get_drag_preview();
			if (drag_preview) {
				drag_preview->set_position(mpos);
			}
			gui.drag_mouse_over = over;
			gui.drag_mouse_over_pos = Vector2();
			
			
			Viewport *embedder = nullptr;
			Vector2 viewport_pos;
			if (is_embedding_subwindows()) {
				embedder = this;
				viewport_pos = mpos;
			} else {
				
				Window *w = Object::cast_to<Window>(this);
				if (w) {
					if (w->is_embedded()) {
						embedder = w->_get_embedder();
						viewport_pos = get_final_transform().xform(mpos) + w->get_position(); 
					}
				}
			}
			Viewport *viewport_under = nullptr;
			if (embedder) {
				
				for (int i = embedder->gui.sub_windows.size() - 1; i >= 0; i--) {
					Window *sw = embedder->gui.sub_windows[i].window;