MINOR: [Ruby] Simplify dense union array RecordBatch creation in tests

[otegami]

Rationale for this change

Addressing TODO comment in test, replace manual construction of DenseUnionArray with direct RecordBatch.new call.

What changes are included in this PR?

This change simplifies the build_record_batch in test/raw-records/test-dense-union-array.rb

Are these changes tested?

Yes

Are there any user-facing changes?

No, this is a test-only change.

[github-actions]

Thanks for opening a pull request!

If this is not a minor PR. Could you open an issue for this pull request on GitHub? https://github.com/apache/arrow/issues/new/choose

Opening GitHub issues ahead of time contributes to the Openness of the Apache Arrow project.

Then could you also rename the pull request title in the following format?

GH-${GITHUB_ISSUE_ID}: [${COMPONENT}] ${SUMMARY}

or

MINOR: [${COMPONENT}] ${SUMMARY}

See also:

• Other pull requests
• Contribution Guidelines - Contributing Overview

[kou]

+1

[conbench-apache-arrow]

After merging your PR, Conbench analyzed the 3 benchmarking runs that have been run so far on merge-commit 01e8a60.

There were 119 benchmark results with an error:

• Commit Run on amd64-m5-4xlarge-linux at 2025-06-19 01:39:09Z
  • tpch (R) with engine=arrow, format=parquet, language=R, memory_map=False, query_id=TPCH-04, scale_factor=10
  • tpch (R) with engine=arrow, format=native, language=R, memory_map=False, query_id=TPCH-12, scale_factor=1
• and 117 more (see the report linked below)

There were no benchmark performance regressions. 🎉

The full Conbench report has more details.