chore: return notFound when disk isn't attached

[guilhem]

https://github.com/kubernetes-sigs/vsphere-csi-driver/blob/5a645a4b2fe29a52bba3305365c5918d049f1cf0/pkg/csi/service/osutils/linux_os_utils.go#L870

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 70.53%. Comparing base (bc68bba) to head (611e6a5).
⚠️ Report is 8 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #393   +/-   ##
=======================================
  Coverage   70.53%   70.53%           
=======================================
  Files          24       24           
  Lines        2118     2118           
=======================================
  Hits         1494     1494           
  Misses        496      496           
  Partials      128      128           

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[guilhem]

⚠️ spec is unclear about what to do here.
Looking at kubernetes code, both return have same action.
This PR could be ignored for now

[guilhem]

Surpassed by #539