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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1. [ ] Does your submission pass tests?
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[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 73.18%. Comparing base (685e341) to head (a4c1f2f).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #393      +/-   ##
==========================================
+ Coverage   73.11%   73.18%   +0.07%     
==========================================
  Files          23       23              
  Lines        2648     2648              
==========================================
+ Hits         1936     1938       +2     
+ Misses        585      583       -2     
  Partials      127      127              

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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