### 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)
Size2 screen_size = _get_camera_screen_size();
				Vector2 screen_endpoints[4] = {
					inv_camera_transform.xform(Vector2(0, 0)),
					inv_camera_transform.xform(Vector2(screen_size.width, 0)),
					inv_camera_transform.xform(Vector2(screen_size.width, screen_size.height)),
					inv_camera_transform.xform(Vector2(0, screen_size.height))
				};
				Transform2D inv_transform = get_global_transform().affine_inverse(); 
				for (int i = 0; i < 4; i++) {
					draw_line(inv_transform.xform(screen_endpoints[i]), inv_transform.xform(screen_endpoints[(i + 1) % 4]), area_axis_color, area_axis_width);
				}
			}
			if (limit_drawing_enabled) {
				Color limit_drawing_color(1, 1, 0.25, 0.63);
				real_t limit_drawing_width = 1;
				if (is_current()) {
					limit_drawing_width = 3;
				}
				Vector2 camera_origin = get_global_position();
				Vector2 camera_scale = get_global_scale().abs();
				Vector2 limit_points[4] = {
					(Vector2(limit[SIDE_LEFT], limit[SIDE_TOP]) - camera_origin) / camera_scale,
					(Vector2(limit[SIDE_RIGHT], limit[SIDE_TOP]) - camera_origin) / camera_scale,
					(Vector2(limit[SIDE_RIGHT], limit[SIDE_BOTTOM]) - camera_origin) / camera_scale,
					(Vector2(limit[SIDE_LEFT], limit[SIDE_BOTTOM]) - camera_origin) / camera_scale
				};
				for (int i = 0; i < 4; i++) {
					draw_line(limit_points[i], limit_points[(i + 1) % 4], limit_drawing_color, limit_drawing_width);
				}
			}