[cherry-pick][1.14]Check whether the volume's source is PVC before fetching its PV.

[blackpiglet]

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Does your change fix a particular issue?

Fixes #7929

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• Accepted the DCO. Commits without the DCO will delay acceptance.
• Created a changelog file or added /kind changelog-not-required as a comment on this pull request.
• Updated the corresponding documentation in site/content/docs/main.

[codecov]

Codecov Report

Attention: Patch coverage is 46.15385% with 7 lines in your changes missing coverage. Please review.

Project coverage is 58.81%. Comparing base (77b3c8f) to head (dcf4e1f).

Files	Patch %	Lines
internal/volumehelper/volume_policy_helper.go	46.15%	5 Missing and 2 partials ⚠️

Additional details and impacted files

@@               Coverage Diff                @@
##           release-1.14    #7976      +/-   ##
================================================
+ Coverage         58.78%   58.81%   +0.02%     
================================================
  Files               346      346              
  Lines             28815    28818       +3     
================================================
+ Hits              16940    16949       +9     
+ Misses            10443    10438       -5     
+ Partials           1432     1431       -1     

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