fix test-buffer-concat.js

[nektro]

pulled out of #15722

[robobun]

^{Updated 7:11 PM PT - Jan 23rd, 2025}

❌ @nektro, your commit 5a25884 has 3 failures in #10420:

• test/regression/issue/09041.test.ts - 1 failing on 🐧 22.04 x64-baseline
• test/js/node/test/parallel/test-http-chunk-problem.js - code 1 on 🐧 3.20 aarch64
• test/js/node/test/parallel/test-http-chunk-problem.js - code 1 on 🐧 22.04 x64
• test/js/node/test/parallel/test-http-chunk-problem.js - code 1 on 🐧 3.20 x64-baseline
• test/js/node/test/parallel/test-http-chunk-problem.js - code 1 on 🐧 22.04 x64-baseline
• test/js/node/dns/node-dns.test.js - 1 failing on 🪟 2019 x64

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🧪   try this PR locally:

bunx bun-pr 16638