src: avoid task runner crash on inaccessible bin paths

[Archkon]

Use the error_code overload of std::filesystem::is_directory() when probing node_modules/.bin, allowing package.json lookup to continue when the directory cannot be accessed.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.29%. Comparing base (a4aa3c0) to head (38bb89c).

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #64905   +/-   ##
=======================================
  Coverage   90.28%   90.29%           
=======================================
  Files         760      760           
  Lines      247061   247062    +1     
  Branches    46592    46587    -5     
=======================================
+ Hits       223058   223081   +23     
+ Misses      15491    15459   -32     
- Partials     8512     8522   +10     

Files with missing lines	Coverage Δ
src/node_task_runner.cc	89.38% <100.00%> (+0.05%)	⬆️

... and 36 files with indirect coverage changes

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