bpo-39573: Use Py_TYPE() macro in Modules directory (GH-18393)

Replace direct access to PyObject.ob_type with Py_TYPE().
diff --git a/Modules/_json.c b/Modules/_json.c
index 3e4fe79..a70043b 100644
--- a/Modules/_json.c
+++ b/Modules/_json.c
@@ -1617,7 +1617,7 @@
         else {
             PyErr_Format(PyExc_TypeError,
                          "keys must be str, int, float, bool or None, "
-                         "not %.100s", key->ob_type->tp_name);
+                         "not %.100s", Py_TYPE(key)->tp_name);
             goto bail;
         }