### 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)
gui.mouse_focus_mask.clear();
								break;
							} else {
								Control *drag_preview = _gui_get_drag_preview();
								if (drag_preview) {
									ERR_PRINT("Don't set a drag preview and return null data. Preview was deleted and drag request ignored.");
									memdelete(drag_preview);
									gui.drag_preview_id = ObjectID();
								}
								gui.dragging = false;
							}
							if (control->data.mouse_filter == Control::MOUSE_FILTER_STOP) {
								break;
							}
						}
						if (ci->is_set_as_top_level()) {
							break;
						}
						ci = ci->get_parent_item();
					}
				}
				gui.drag_attempted = true;
				if (gui.dragging) {
					_propagate_viewport_notification(this, NOTIFICATION_DRAG_BEGIN);
				}
			}
		}
		Control *over = nullptr;
		if (gui.mouse_in_viewport) {
			over = gui_find_control(mpos);