refcounting bug in add_subclass in typeobject.c

[kumaraditya303]

Currently is does not decref key and ref when the created dict is null.
See #93989

[Fidget-Spinner]

Seems like this bug also exists in 3.11 and 3.10. Could you work on the 3.10 backport please? I think it needs to be done manually.

[kumaraditya303]

Okay, I'll create the backports.