bpo-39573: Use Py_TYPE() macro in Objects directory (GH-18392)

Replace direct access to PyObject.ob_type with Py_TYPE().
diff --git a/Objects/cellobject.c b/Objects/cellobject.c
index 911cf52..e97feef 100644
--- a/Objects/cellobject.c
+++ b/Objects/cellobject.c
@@ -112,7 +112,7 @@
         return PyUnicode_FromFormat("<cell at %p: empty>", op);
 
     return PyUnicode_FromFormat("<cell at %p: %.80s object at %p>",
-                               op, op->ob_ref->ob_type->tp_name,
+                               op, Py_TYPE(op->ob_ref)->tp_name,
                                op->ob_ref);
 }