bpo-37648: Fixed minor inconsistency in some __contains__. (GH-14904)

The collection's item is now always at the left and
the needle is on the right of ==.

Objects/abstract.c

@@ -2016,7 +2016,7 @@ _PySequence_IterSearch(PyObject *seq, PyObject *obj, int operation)
             break;
         }
 
-        cmp = PyObject_RichCompareBool(obj, item, Py_EQ);
+        cmp = PyObject_RichCompareBool(item, obj, Py_EQ);
         Py_DECREF(item);
         if (cmp < 0)
             goto Fail;