Alternate fix for bun --bun folder

[pfgithub]

What does this PR do?

Alternative for #15117. Sets CWD & fixes bun --bun run build, does not fix bun test.todo and does not support bun index (for index.ts)

Test failures:

• next-build.test.ts

[robobun]

^{Updated 9:09 PM PT - Jan 17th, 2025}

❌ @pfgithub, your commit 5c90494 has 1 failures in #10001:

• test/integration/next-pages/test/next-build.test.ts - 1 failing on 🪟 2019 x64-baseline
• test/integration/next-pages/test/next-build.test.ts - 1 failing on 🪟 2019 x64

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🧪   try this PR locally:

bunx bun-pr 16492