### 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)
ClassDB::bind_method(D_METHOD("set_size", "size"), &SubViewport::set_size);
	ClassDB::bind_method(D_METHOD("get_size"), &SubViewport::get_size);
	ClassDB::bind_method(D_METHOD("set_size_2d_override", "size"), &SubViewport::set_size_2d_override);
	ClassDB::bind_method(D_METHOD("get_size_2d_override"), &SubViewport::get_size_2d_override);
	ClassDB::bind_method(D_METHOD("set_size_2d_override_stretch", "enable"), &SubViewport::set_size_2d_override_stretch);
	ClassDB::bind_method(D_METHOD("is_size_2d_override_stretch_enabled"), &SubViewport::is_size_2d_override_stretch_enabled);
	ClassDB::bind_method(D_METHOD("set_update_mode", "mode"), &SubViewport::set_update_mode);
	ClassDB::bind_method(D_METHOD("get_update_mode"), &SubViewport::get_update_mode);
	ClassDB::bind_method(D_METHOD("set_clear_mode", "mode"), &SubViewport::set_clear_mode);
	ClassDB::bind_method(D_METHOD("get_clear_mode"), &SubViewport::get_clear_mode);
	ADD_PROPERTY(PropertyInfo(Variant::VECTOR2I, "size", PROPERTY_HINT_NONE, "suffix:px"), "set_size", "get_size");
	ADD_PROPERTY(PropertyInfo(Variant::VECTOR2I, "size_2d_override", PROPERTY_HINT_NONE, "suffix:px"), "set_size_2d_override", "get_size_2d_override");
	ADD_PROPERTY(PropertyInfo(Variant::BOOL, "size_2d_override_stretch"), "set_size_2d_override_stretch", "is_size_2d_override_stretch_enabled");
	ADD_GROUP("Render Target", "render_target_");
	ADD_PROPERTY(PropertyInfo(Variant::INT, "render_target_clear_mode", PROPERTY_HINT_ENUM, "Always,Never,Next Frame"), "set_clear_mode", "get_clear_mode");
	ADD_PROPERTY(PropertyInfo(Variant::INT, "render_target_update_mode", PROPERTY_HINT_ENUM, "Disabled,Once,When Visible,When Parent Visible,Always"), "set_update_mode", "get_update_mode");
	BIND_ENUM_CONSTANT(CLEAR_MODE_ALWAYS);
	BIND_ENUM_CONSTANT(CLEAR_MODE_NEVER);
	BIND_ENUM_CONSTANT(CLEAR_MODE_ONCE);
	BIND_ENUM_CONSTANT(UPDATE_DISABLED);
	BIND_ENUM_CONSTANT(UPDATE_ONCE);
	BIND_ENUM_CONSTANT(UPDATE_WHEN_VISIBLE);
	BIND_ENUM_CONSTANT(UPDATE_WHEN_PARENT_VISIBLE);
	BIND_ENUM_CONSTANT(UPDATE_ALWAYS);
}
SubViewport::SubViewport() {
	RS::get_singleton()->viewport_set_size(get_viewport_rid(), get_size().width, get_size().height);
}
SubViewport::~SubViewport() {}