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/methodobject.c b/Objects/methodobject.c
index 6a37238..2a8111f 100644
--- a/Objects/methodobject.c
+++ b/Objects/methodobject.c
@@ -234,7 +234,7 @@
                                    m->m_ml->ml_name);
     return PyUnicode_FromFormat("<built-in method %s of %s object at %p>",
                                m->m_ml->ml_name,
-                               m->m_self->ob_type->tp_name,
+                               Py_TYPE(m->m_self)->tp_name,
                                m->m_self);
 }