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/listobject.c

@@ -449,8 +449,7 @@ list_contains(PyListObject *a, PyObject *el)
     int cmp;
 
     for (i = 0, cmp = 0 ; cmp == 0 && i < Py_SIZE(a); ++i)
-        cmp = PyObject_RichCompareBool(el, PyList_GET_ITEM(a, i),
-                                           Py_EQ);
+        cmp = PyObject_RichCompareBool(PyList_GET_ITEM(a, i), el, Py_EQ);
     return cmp;
 }