fs: check subdir correctly in cpSync

[jazelly]

Fixes: #54285

[jazelly]

This probably will have merge conflicts with #54653. I'd like the other one to land first as this one is easier to rebase, re-review and re-approve, if that sounds good : )

[RedYetiDev]

Per the comment above, I've added blocked, however, feel free to adjust.

[codecov]

Codecov Report

Attention: Patch coverage is 80.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 88.24%. Comparing base (8b8fc53) to head (b654965).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
src/node_file.cc	80.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #55033   +/-   ##
=======================================
  Coverage   88.23%   88.24%           
=======================================
  Files         652      652           
  Lines      183855   183859    +4     
  Branches    35856    35852    -4     
=======================================
+ Hits       162227   162238   +11     
+ Misses      14909    14903    -6     
+ Partials     6719     6718    -1     

Files with missing lines	Coverage Δ
src/node_file.cc	77.05% <80.00%> (-0.05%)	⬇️

... and 29 files with indirect coverage changes

[jakecastelli]

cc. @nodejs/fs @anonrig @aduh95 (surprised that both of you aren't in the fs team 😄)