Improve promise rejections handling in hardhat/async-test-sanity.js

[ursulabauer]

I've fixed the issue with unhandled promise rejections by ensuring proper error handling.
The updated code now preserves error context, making debugging easier and improving overall reliability.

I've also added comments to clarify the changes.

PR Checklist

• Tests
• Documentation
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Latest commit: 2566b5f

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