fix: chunk render cache panic on css extract diagnostics

[ahabhgk]

Summary

Don't cache diagnostics for chunk render cache

Checklist

• Tests updated (or not required).
• Documentation updated (or not required).

[netlify]

✅ Deploy Preview for rspack canceled.

Name	Link
🔨 Latest commit	47c8854
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[codspeed-hq]

CodSpeed Performance Report

Merging #8562 will not alter performance

_{Comparing fix-chunk-render-cache-css-panic (47c8854) with main (21edaba)}

Summary

✅ 1 untouched benchmarks