Remove PVC's selector in backup's PVC action.

[blackpiglet]

Thank you for contributing to Velero!

Please add a summary of your change

Does your change fix a particular issue?

Fixes #6444

Please indicate you've done the following:

• 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-commenter]

Codecov Report

Merging #6481 (732d3ff) into main (49e8058) will increase coverage by 0.00%.
The diff coverage is 0.00%.

❗ Current head 732d3ff differs from pull request most recent head 1a6ef0f. Consider uploading reports for the commit 1a6ef0f to get more accurate results

@@           Coverage Diff           @@
##             main    #6481   +/-   ##
=======================================
  Coverage   60.03%   60.04%           
=======================================
  Files         229      229           
  Lines       24491    24489    -2     
=======================================
  Hits        14704    14704           
+ Misses       8774     8772    -2     
  Partials     1013     1013           

Impacted Files	Coverage Δ
pkg/backup/backup_pv_action.go	45.71% <0.00%> (+2.47%)	⬆️

[reasonerjt]

Can we make sure the removal of labelSelector only happens when the restore will be done via dynamic provision? (podvolume, CSI).

[reasonerjt]

Approving the PR to unblock merging it, I'm fine the cosmetic code change be applied afterwards