message: Fix _Arg op diagnostic for _handle_dtypes attribute
  Fix typo in _Arg op diagnostic for _handle_dtypes attribute.
diff: @@ -67,7 +67,7 @@ REGISTER_SYSTEM_OP("_Arg")
  if (dtype_attr->list().type().empty()) {
  return errors::InvalidArgument(
  "Invalid \"_handle_dtypes\" attribute value for _Arg node: ",
  - shape_attr->DebugString());
  + dtype_attr->DebugString());
  }
  if (shape_attr->list().shape().empty()) {
  return errors::InvalidArgument(
  