Add more UT for the CSI plugins.

[blackpiglet]

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Does your change fix a particular issue?

Fixes #(issue)

Please indicate you've done the following:

• [x] 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[bot]]

Codecov Report

Attention: Patch coverage is 91.66667% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 63.35%. Comparing base (c888f51) to head (d3cc42d).

Files	Patch %	Lines
pkg/restore/actions/csi/volumesnapshot_action.go	90.00%	1 Missing :warning:
pkg/util/csi/volume_snapshot.go	0.00%	0 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #7661 +/- ## ========================================== + Coverage 61.29% 63.35% +2.06% ========================================== Files 276 278 +2 Lines 31490 24952 -6538 ========================================== - Hits 19301 15808 -3493 + Misses 10830 7767 -3063 - Partials 1359 1377 +18 ```

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