Use Py_NewRef in Modules/_struct.c (GH-23981)

Modules/_struct.c

@@ -1442,8 +1442,7 @@
     self = alloc_func(type, 0);
     if (self != NULL) {
         PyStructObject *s = (PyStructObject*)self;
-        Py_INCREF(Py_None);
-        s->s_format = Py_None;
+        s->s_format = Py_NewRef(Py_None);
         s->s_codes = NULL;
         s->s_size = -1;
         s->s_len = -1;