### 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)
mb->set_position(pos);
#ifdef DEBUG_ENABLED
			if (EngineDebugger::get_singleton() && gui.mouse_focus) {
				Array arr;
				arr.push_back(gui.mouse_focus->get_path());
				arr.push_back(gui.mouse_focus->get_class());
				EngineDebugger::get_singleton()->send_message("scene:click_ctrl", arr);
			}
#endif
			if (mb->get_button_index() == MouseButton::LEFT) { 
				CanvasItem *ci = gui.mouse_focus;
				while (ci) {
					Control *control = Object::cast_to<Control>(ci);
					if (control) {
						if (control->get_focus_mode() != Control::FOCUS_NONE) {
							if (control != gui.key_focus) {
								control->grab_focus();
							}
							break;
						}
						if (control->data.mouse_filter == Control::MOUSE_FILTER_STOP) {
							break;
						}
					}
					if (ci->is_set_as_top_level()) {
						break;
					}
					ci = ci->get_parent_item();
				}
			}