gh-145064: Fix JIT assertion failure during CALL_ALLOC_AND_ENTER_INIT side exit

[cocolato]

When CALL_ALLOC_AND_ENTER_INIT creates an instance of a heap type (with __slots__ and tp_new == object.__new__), it pushes a shim frame via _PyFrame_PushTrampolineUnchecked. This shim frame has f_funcobj = Py_None:

cpython/Include/internal/pycore_interpframe.h

Line 368 in 2be2dd5

frame->f_funcobj = PyStackRef_None;

If a JIT trace runs out of buffer space exactly at this shim frame's EXIT_INIT_CHECK instruction, the _EXIT_TRACE terminator hands off to a _COLD_EXIT executor, which calls _PyJit_TryInitializeTracing() with the shim frame. The existing guard only checked func == NULL, but Py_None is not NULL, so control falls through which casue assertion crash.

• Issue: JIT: co != NULL assertion failure in *_Py_uop_frame_new #145064

[cocolato]

cc @Fidget-Spinner