[cherry-pick]Fix backup post hook issue

[ywk253100]

Fix backup post hook issue

Fixes #8159

Thank you for contributing to Velero!

Please add a summary of your change

Does your change fix a particular issue?

Fixes #(issue)

Please indicate you've done the following:

• Accepted the DCO. Commits without the DCO will delay acceptance.
• Created a changelog file (make new-changelog) or comment /kind changelog-not-required on this PR.
• Updated the corresponding documentation in site/content/docs/main.

[codecov]

Codecov Report

Attention: Patch coverage is 55.71429% with 31 lines in your changes missing coverage. Please review.

Project coverage is 59.10%. Comparing base (f0001a5) to head (fe8c086).
Report is 2 commits behind head on release-1.15.

Files with missing lines	Patch %	Lines
pkg/backup/backup.go	52.30%	26 Missing and 5 partials ⚠️

Additional details and impacted files

@@               Coverage Diff                @@
##           release-1.15    #8517      +/-   ##
================================================
- Coverage         59.13%   59.10%   -0.04%     
================================================
  Files               367      367              
  Lines             39059    39118      +59     
================================================
+ Hits              23099    23122      +23     
- Misses            14496    14527      +31     
- Partials           1464     1469       +5     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.