os: freeze signals constant

[Xstoudi]

Remove the ability to mutate signals constant as doing so can lead to unexpected behavior, notably when spawning child process.

Fixes: #44749

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.52%. Comparing base (81e05e1) to head (55ff2a1).
⚠️ Report is 36 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #61038      +/-   ##
==========================================
- Coverage   88.53%   88.52%   -0.02%     
==========================================
  Files         703      703              
  Lines      208538   208541       +3     
  Branches    40224    40221       -3     
==========================================
- Hits       184629   184606      -23     
- Misses      15912    15961      +49     
+ Partials     7997     7974      -23     

Files with missing lines	Coverage Δ
lib/os.js	98.60% <100.00%> (+0.01%)	⬆️

... and 42 files with indirect coverage changes

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[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/70576/

[nodejs-github-bot]

Landed in 472f586