### 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)
String tooltip = _gui_get_tooltip(over, gui.tooltip_control->get_global_transform().xform_inv(mpos));
						tooltip = tooltip.strip_edges();
						if (tooltip.length() == 0) {
							_gui_cancel_tooltip();
						} else if (gui.tooltip_label) {
							if (tooltip == gui.tooltip_label->get_text()) {
								is_tooltip_shown = true;
							}
						} else {
							is_tooltip_shown = true; 
						}
					} else {
						_gui_cancel_tooltip();
					}
				}
				if (!is_tooltip_shown && over->can_process()) {
					if (gui.tooltip_timer.is_valid()) {
						gui.tooltip_timer->release_connections();
						gui.tooltip_timer = Ref<SceneTreeTimer>();
					}
					gui.tooltip_control = over;
					gui.tooltip_pos = over->get_screen_transform().xform(pos);
					gui.tooltip_timer = get_tree()->create_timer(gui.tooltip_delay);
					gui.tooltip_timer->set_ignore_time_scale(true);
					gui.tooltip_timer->connect("timeout", callable_mp(this, &Viewport::_gui_show_tooltip));
				}
			}
			mm->set_position(pos);
			Control::CursorShape cursor_shape = Control::CURSOR_ARROW;
			{