fix(serveStatic): ensure etag header is set before sending 304 response

[stafyniaksacha]

🔗 Linked issue

❓ 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 small fix to ensure ETag header is set before sending 304 response: https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/304

The response [...] must include the headers that would have been sent in an equivalent 200 OK response: Cache-Control, Content-Location, Date, ETag, Expires, and Vary.

📝 Checklist

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

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (e38d444) 77.83% compared to head (d6eff87) 77.83%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #653   +/-   ##
=======================================
  Coverage   77.83%   77.83%           
=======================================
  Files          47       47           
  Lines        4286     4286           
  Branches      611      608    -3     
=======================================
  Hits         3336     3336           
  Misses        933      933           
  Partials       17       17           

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[pi0]

Thanks!