### 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)
camera_3d_set.insert(p_camera);
	return camera_3d_set.size() == 1;
}
void Viewport::_camera_3d_remove(Camera3D *p_camera) {
	camera_3d_set.erase(p_camera);
	if (camera_3d == p_camera) {
		camera_3d->notification(Camera3D::NOTIFICATION_LOST_CURRENT);
		camera_3d = nullptr;
	}
}
void Viewport::_camera_3d_make_next_current(Camera3D *p_exclude) {
	for (Camera3D *E : camera_3d_set) {
		if (p_exclude == E) {
			continue;
		}
		if (!E->is_inside_tree()) {
			continue;
		}
		if (camera_3d != nullptr) {
			return;
		}
		E->make_current();
	}
}
void Viewport::enable_camera_3d_override(bool p_enable) {