### 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)
ERR_FAIL_INDEX(p_msaa, MSAA_MAX);
	if (msaa_3d == p_msaa) {
		return;
	}
	msaa_3d = p_msaa;
	RS::get_singleton()->viewport_set_msaa_3d(viewport, RS::ViewportMSAA(p_msaa));
}
Viewport::MSAA Viewport::get_msaa_3d() const {
	return msaa_3d;
}
void Viewport::set_screen_space_aa(ScreenSpaceAA p_screen_space_aa) {
	ERR_FAIL_INDEX(p_screen_space_aa, SCREEN_SPACE_AA_MAX);
	if (screen_space_aa == p_screen_space_aa) {
		return;
	}
	screen_space_aa = p_screen_space_aa;
	RS::get_singleton()->viewport_set_screen_space_aa(viewport, RS::ViewportScreenSpaceAA(p_screen_space_aa));
}
Viewport::ScreenSpaceAA Viewport::get_screen_space_aa() const {
	return screen_space_aa;
}
void Viewport::set_use_taa(bool p_use_taa) {
	if (use_taa == p_use_taa) {
		return;
	}
	use_taa = p_use_taa;
	RS::get_singleton()->viewport_set_use_taa(viewport, p_use_taa);
}
bool Viewport::is_using_taa() const {