fix: try rs test run in single thread

[IWANABETHATGUY]

Summary

1. Try to fix random test fail and retry success
   here is the time cost between test-threads=1, and test-threads=${defualt-value}
2. Notice that our rspack is still running in multi-thread, this change only makes the testing tasks run in single thread.

default

test-threds=1

Related issue (if exists)

Types of changes

• Docs change / Dependency upgrade
• Bug fix
• New feature / Improvement
• Refactoring
• Breaking change

Checklist

• I have added changeset via pnpm run changeset.
• I have added tests to cover my changes.

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Latest commit: 1388a87

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