test(proxy): add additional test to make sure json response is sent as is

[Aareksio]

🔗 Linked issue

unjs/nitro#1605

❓ Type of change

• 📖 Documentation (updates to the documentation, readme, or JSdoc annotations)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

This is a passing test to confirm the issue with proxy applying pretty-print to JSON is caused by downstream (nitro).

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.

[codecov]

Codecov Report

Merging #512 (3e062d6) into main (8af0474) will not change coverage.
The diff coverage is n/a.

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##             main     #512   +/-   ##
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  Coverage   82.11%   82.11%           
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  Files          31       31           
  Lines        3646     3646           
  Branches      536      539    +3     
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  Hits         2994     2994           
  Misses        652      652