src: return failure when task spawning fails

[Archkon]

Set a non-zero exit code and return immediately when uv_spawn() fails, since no process exit callback will be invoked.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.29%. Comparing base (93b1088) to head (553a48b).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/node_task_runner.cc	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #64956      +/-   ##
==========================================
+ Coverage   90.27%   90.29%   +0.01%     
==========================================
  Files         760      760              
  Lines      247137   247138       +1     
  Branches    46612    46621       +9     
==========================================
+ Hits       223111   223152      +41     
+ Misses      15497    15454      -43     
- Partials     8529     8532       +3     

Files with missing lines	Coverage Δ
src/node_task_runner.cc	88.82% <0.00%> (-0.50%)	⬇️

... and 31 files with indirect coverage changes

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[avivkeller]

What was the old behavior? Silently return?

If so, is this kind of a breaking change?

[Archkon]

@avivkeller Not really, the old behavior just print error but wrongly mark exit_code as success