child_process: treat ipc length header as unsigned uint32

[islandryu]

Fixes: #61312

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.53%. Comparing base (5d9855b) to head (180643a).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #61344   +/-   ##
=======================================
  Coverage   88.52%   88.53%           
=======================================
  Files         704      704           
  Lines      208739   208739           
  Branches    40280    40277    -3     
=======================================
+ Hits       184787   184802   +15     
+ Misses      15969    15932   -37     
- Partials     7983     8005   +22     

Files with missing lines	Coverage Δ
lib/internal/child_process/serialization.js	95.85% <100.00%> (ø)

... and 45 files with indirect coverage changes

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[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/70773/