Fix comment about PyObject_IsTrue. (GH-22343)

The `for` statement doesn't use a condition and this function, the `while` statement does.

Objects/object.c

@@ -1387,7 +1387,7 @@ PyObject_GenericSetDict(PyObject *obj, PyObject *value, void *context)
 }
 
 
-/* Test a value used as condition, e.g., in a for or if statement.
+/* Test a value used as condition, e.g., in a while or if statement.
    Return -1 if an error occurred */
 
 int