checkout: ensure subdirs are deleted before parent dir

[baleian]

Fixes iterative/dvc/#4344

[baleian]

Hi @skshetry ,

For more information, analysis of the linked issue's cause revealed the following:
during the deletion of deleted_dirs, if the process attempts to delete a parent directory before removing its nested children first, this deletion attempt is ignored by the try-catch block. This occurs because the parent directory is not yet empty.

To prevent this, we now perform reverse sorting beforehand to ensure that child directories targeted for removal are attempted first.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.53%. Comparing base (e38c8c2) to head (69f9ce0).
Report is 19 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #601      +/-   ##
==========================================
+ Coverage   72.42%   73.53%   +1.10%     
==========================================
  Files          67       66       -1     
  Lines        5132     5037      -95     
  Branches      605      588      -17     
==========================================
- Hits         3717     3704      -13     
+ Misses       1227     1144      -83     
- Partials      188      189       +1     

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[skshetry]

Thank you for contributing. :)