ci: increase mac test parallelism to 7

[nektro]

testing this out
job capacity is fixed but this will make individual jobs complete much faster and make a timeout less of an impact

[robobun]

^{Updated 8:20 PM PT - Jul 31st, 2025}

❌ @nektro, your commit 6f46c1c has 6 failures in Build #21931:

• test/js/sql/sql.test.ts - 1 failing on 🐧 24.04 x64
• test/integration/mysql2/mysql2.test.ts - timeout on 🍎 14 aarch64
• test/js/third_party/next-auth/next-auth.test.ts - 1 failing on 🪟 2019 x64
• test/js/third_party/next-auth/next-auth.test.ts - 1 failing on 🪟 2019 x64-baseline
[webpack.cache.PackFileCacheStrategy] Caching failed for pack: RangeError: Out of memory
• test/js/bun/util/inspect-error-leak.test.js - 1 failing on 🐧 12 x64-asan
• test/js/node/test/parallel/test-child-process-spawnsync-shell.js - timeout on 🪟 2019 x64-baseline
• test/js/node/test/parallel/test-child-process-spawnsync-shell.js - timeout on 🪟 2019 x64
• test/js/bun/s3/s3.leak.test.ts - 2 failing on 🐧 12 x64-asan

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🧪   To try this PR locally:

bunx bun-pr 21530

That installs a local version of the PR into your bun-21530 executable, so you can run:

bun-21530 --bun