message: test: fix test "test_prepare_uncles"; it could failed with a very small chance
diff: @@ -201,7 +201,7 @@ fn test_prepare_uncles() {
  .unwrap()
  .unwrap();
  // block number 3, epoch 0
  - while (Into::<u64>::into(block_template.number)) != 3 {
  + while (Into::<u64>::into(block_template.number)) != 3 || block_template.uncles.is_empty() {
  block_template = tx_pool
  .get_block_template(None, None, None)
  .unwrap()
  