GH-46820: [CI][Integration] Use Node.js 20 by default

[kou]

Rationale for this change

We're using NODE=XX in .env as the default Node.js version.

What changes are included in this PR?

Use NODE=20 in .env.

Are these changes tested?

Yes.

Are there any user-facing changes?

No.

• GitHub Issue: [CI][Integration] Use Node.js 20 by default #46820

[github-actions]

⚠️ GitHub issue #46820 has been automatically assigned in GitHub to PR creator.

[kou]

https://github.com/apache/arrow/actions/runs/15670314882/job/44141128787?pr=46821#step:12:305

  #8 22.41   nodejs-20.18.1-hc55a1b2_0.conda                       17MB

Node.js 20 was used.

[raulcd]

Integration job is flaky but does not seem related to the PR. It has been flaky for a while, we should probably open an issue and investigate where the flakyness is coming from.

[conbench-apache-arrow]

After merging your PR, Conbench analyzed the 3 benchmarking runs that have been run so far on merge-commit a974df4.

There were 122 benchmark results with an error:

• Commit Run on arm64-t4g-2xlarge-linux at 2025-06-16 09:58:50Z
  • tpch (R) with engine=arrow, format=parquet, language=R, memory_map=False, query_id=TPCH-07, scale_factor=1
  • tpch (R) with engine=arrow, format=native, language=R, memory_map=False, query_id=TPCH-09, scale_factor=1
• and 120 more (see the report linked below)

There were no benchmark performance regressions. 🎉

The full Conbench report has more details.