fix: forward-compatibility adaptation for request headers

[efdali]

What's this PR do?

• • when we started to use node 18, headers were coming as undefined. we realized that it was caused by these changes on nodejs.

Where should the reviewer start?

How should this be manually tested?

Any background context you want to provide?

• • you can find more details in this issue

What are the relevant tickets?

Screenshots (if appropriate)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (e858095) 91.46% compared to head (1796ece) 91.51%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #407      +/-   ##
==========================================
+ Coverage   91.46%   91.51%   +0.05%     
==========================================
  Files          27       27              
  Lines        1827     1827              
  Branches      398      398              
==========================================
+ Hits         1671     1672       +1     
+ Misses        156      155       -1     

Files	Coverage Δ
src/fragment.ts	93.21% <100.00%> (ø)

... and 1 file with indirect coverage changes

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[yunusemredilber]

Thanks 🌸