message: Reduced heap usage in unit test
diff: @@ -683,7 +683,7 @@ mod tests {
  };
  {
  - let mut index_writer = index.writer_with_num_threads(1, 40_000_000).unwrap();
  + let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
  {
  // writing the segment
  {
  @@ -733,7 +733,7 @@ mod tests {
  let segment_ids = index
  .searchable_segment_ids()
  .expect("Searchable segments failed.");
  - let mut index_writer = index.writer_with_num_threads(1, 40_000_000).unwrap();
  + let mut index_writer = index.writer_with_num_threads(1, 3_000_000).unwrap();
  index_writer
  .merge(&segment_ids)
  .wait()
  