Message 390567 - Python tracker

> We could also adjust Parser/asdl_c.py to decref right after a failed _PyArena_AddPyObject() call, instead of goto failure and Py_XDECREF. I'm not sure it's worth it though.

I normally recommend having the least amount of exist paths possible, makes reasoning easily normally at the cost of some extra NULL checks for the XDECREF in failure scenarios