message: correctly call ek::schedule in array-to-string code
diff: @@ -149,7 +149,7 @@ struct StringBuffer {
  if (!detail::put_shape(value, shape)) {
  put("[ragged array]");
  } else {
  - enoki::schedule(shape);
  + enoki::schedule(value.derived());
  detail::to_string<true>(*this, value.derived(), shape);
  }
  