fix(cache): fix etag and last-modified values

[pi0]

🔗 Linked issue

resolves #1850

❓ 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 fixes default values to be applied before normalizing header types to string

📝 Checklist

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

[codecov]

Codecov Report

Merging #1855 (7250f71) into main (e37359c) will decrease coverage by 0.24%.
Report is 1 commits behind head on main.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##             main    #1855      +/-   ##
==========================================
- Coverage   52.35%   52.12%   -0.24%     
==========================================
  Files         170      170              
  Lines       11777    11780       +3     
  Branches      907      901       -6     
==========================================
- Hits         6166     6140      -26     
- Misses       5515     5544      +29     
  Partials       96       96              

Files	Coverage Δ
src/runtime/cache.ts	0.00% <0.00%> (ø)

... and 2 files with indirect coverage changes