[LEP-2004] fix(disk): "findmnt" fallback for missing fstype, increase test coverage

[gyuho]

Signed-off-by: Gyuho Lee gyuhol@nvidia.com

[codecov]

Codecov Report

❌ Patch coverage is 68.83117% with 24 lines in your changes missing coverage. Please review.
✅ Project coverage is 67.10%. Comparing base (68139d1) to head (66ddc49).
⚠️ Report is 14 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/disk/lsblk.go	68.83%	23 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1059      +/-   ##
==========================================
+ Coverage   66.69%   67.10%   +0.40%     
==========================================
  Files         314      314              
  Lines       26571    26617      +46     
==========================================
+ Hits        17722    17861     +139     
+ Misses       7961     7873      -88     
+ Partials      888      883       -5     

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