gh-130920: Fix data race in STORE_SUBSCR_LIST_INT (#130923)

The write of the item to the list needs to use an atomic operation in
the free threading build.

Co-authored-by: Tomasz Pytel <tompytel@gmail.com>

Python/bytecodes.c

@@ -1015,7 +1015,8 @@ dummy_func(
             STAT_INC(STORE_SUBSCR, hit);
 
             PyObject *old_value = PyList_GET_ITEM(list, index);
-            PyList_SET_ITEM(list, index, PyStackRef_AsPyObjectSteal(value));
+            FT_ATOMIC_STORE_PTR_RELEASE(_PyList_ITEMS(list)[index],
+                                        PyStackRef_AsPyObjectSteal(value));
             assert(old_value != NULL);
             UNLOCK_OBJECT(list);  // unlock before decrefs!
             PyStackRef_CLOSE_SPECIALIZED(sub_st, _PyLong_ExactDealloc);