Using SubViewport with own_world_3d = true causes memory leak.

[MizunagiKB]

Godot version

v4.1.1.stable.official [bd6af8e]

System information

Godot v4.1.1.stable - macOS 13.5.2 - Vulkan (Forward+) - integrated Apple M2 Max - Apple M2 Max (12 Threads)

Issue description

Memory allocated when using SubViewport with own_world_3d = true is not released when own_world_3d = false or queue_free.

The set_use_own_world_3d function is called when own_world_3d is changed.
When true is given, it seems that own_world_3d is created, but the opportunity to destroy it is not given.

Steps to reproduce

This bug can be reproduced with the following code.

func _process(delta):

    var v = SubViewport.new()

    for n in range(128):
        v.own_world_3d = true
        v.own_world_3d = false

    v.queue_free()

Minimal reproduction project

viewport_memory_leak.zip

[TokageItLab]

I investigated this a bit and it seems that the memory freeing by unref() for World3D is not working properly in the first place.