_PyObject_XDecRefDelayed() should handle immortal objects #159431

Bug report

The callers of _PyObject_XDecRefDelayed() currently check if an object is immortal. However, that's insufficient, since the object could become immortal after it's queued and before the queue is processed. That triggers an assertion failure in debug builds. In release builds the object silently becomes mortal. The check has to happen when the queue is processed.

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Linked PRs

• gh-159431: Handle immortal objects in _PyObject_XDecRefDelayed() #159433