### 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)
Control *c = over;
				Vector2 cpos = pos;
				while (c) {
					if (!gui.mouse_focus_mask.is_empty() || c->has_point(cpos)) {
						cursor_shape = c->get_cursor_shape(cpos);
					} else {
						cursor_shape = Control::CURSOR_ARROW;
					}
					cpos = c->get_transform().xform(cpos);
					if (cursor_shape != Control::CURSOR_ARROW) {
						break;
					}
					if (c->data.mouse_filter == Control::MOUSE_FILTER_STOP) {
						break;
					}
					if (c->is_set_as_top_level()) {
						break;
					}
					c = c->get_parent_control();
				}
			}
			ds_cursor_shape = (DisplayServer::CursorShape)cursor_shape;
			bool stopped = false;
			if (over && over->can_process()) {
				stopped = _gui_call_input(over, mm);
			}
			if (stopped) {
				set_input_as_handled();
			}
		}