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 90.31%. Comparing base (73236f3) to head (71936e7).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #64905   +/-   ##
=======================================
  Coverage   90.31%   90.31%           
=======================================
  Files         759      759           
  Lines      248295   248296    +1     
  Branches    46863    46859    -4     
=======================================
+ Hits       224242   224251    +9     
- Misses      15460    15470   +10     
+ Partials     8593     8575   -18     

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

... and 28 files with indirect coverage changes

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