dynamic binding issue with _io.BytesIO/_io.StringIO #1004
Description
The following error comes up when running CPython.test_memoryio.test_instance_dict_leak:
TypeError: The result type 'System.Int32' of the dynamic binding produced by the object with type 'IronPython.Modules.PythonIOModule+StringIO' for the binder 'Python SetMember foo' is not compatible with the result type 'System.Object' expected by the call site.