src: override inherited task runner environment

[Archkon]

Filter inherited NODE_RUN_SCRIPT_NAME and NODE_RUN_PACKAGE_JSON_PATH before adding the current task values. This prevents duplicate environment entries during nested node --run invocations.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.30%. Comparing base (a4aa3c0) to head (86ee17a).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #64906      +/-   ##
==========================================
+ Coverage   90.28%   90.30%   +0.01%     
==========================================
  Files         760      760              
  Lines      247061   247065       +4     
  Branches    46592    46586       -6     
==========================================
+ Hits       223058   223108      +50     
+ Misses      15491    15441      -50     
- Partials     8512     8516       +4     

Files with missing lines	Coverage Δ
src/node_task_runner.cc	89.01% <100.00%> (-0.32%)	⬇️

... and 33 files with indirect coverage changes

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