message: Fix calculation of execution results' root hash.
  The previous logic would "double serialize" the inner elements:
  1. ExecutionResult -> Vec<u8>
  2. When serializing outer vector we would prepend length of each inner
  vectors before writing its bytes.
diff: @@ -408,12 +408,9 @@ where
  fn compute_execution_results_root_hash<'a>(
  results: &mut impl Iterator<Item = &'a ExecutionResult>,
  ) -> Result<Digest, BlockCreationError> {
  - let mut execution_results_serialized = vec![];
  - for result in results {
  - execution_results_serialized
  - .push(result.to_bytes().map_err(BlockCreationError::BytesRepr)?);
  - }
  - let execution_results_bytes = execution_results_serialized
  + let execution_results_bytes = results
  + .cloned()
  + .collect::<Vec<_>>()
  .to_bytes()
  .map_err(BlockCreationError::BytesRepr)?;
  Ok(Digest::hash_bytes_into_chunks_if_necessary(
  