### 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)
return gui.embed_subwindows_hint;
}
void Viewport::pass_mouse_focus_to(Viewport *p_viewport, Control *p_control) {
	ERR_FAIL_NULL(p_viewport);
	ERR_FAIL_NULL(p_control);
	if (gui.mouse_focus) {
		p_viewport->gui.mouse_focus = p_control;
		p_viewport->gui.mouse_focus_mask = gui.mouse_focus_mask;
		p_viewport->gui.key_focus = p_control;
		p_viewport->gui.forced_mouse_focus = true;
		gui.mouse_focus = nullptr;
		gui.forced_mouse_focus = false;
		gui.mouse_focus_mask.clear();
	}
}
void Viewport::set_sdf_oversize(SDFOversize p_sdf_oversize) {
	ERR_FAIL_INDEX(p_sdf_oversize, SDF_OVERSIZE_MAX);
	sdf_oversize = p_sdf_oversize;
	RS::get_singleton()->viewport_set_sdf_oversize_and_scale(viewport, RS::ViewportSDFOversize(sdf_oversize), RS::ViewportSDFScale(sdf_scale));
}
Viewport::SDFOversize Viewport::get_sdf_oversize() const {
	return sdf_oversize;
}
void Viewport::set_sdf_scale(SDFScale p_sdf_scale) {
	ERR_FAIL_INDEX(p_sdf_scale, SDF_SCALE_MAX);
	sdf_scale = p_sdf_scale;
	RS::get_singleton()->viewport_set_sdf_oversize_and_scale(viewport, RS::ViewportSDFOversize(sdf_oversize), RS::ViewportSDFScale(sdf_scale));
}
Viewport::SDFScale Viewport::get_sdf_scale() const {