Fixed backup of non default upload directory

What does this MR do?

This MR fixes an major bug, which occurs, when uploads_storage_path is set to an different path than default.

e.g: gitlab_rails['uploads_storage_path'] = "/git/gitlab-data/uploads"

Thanks to @deepbluev7 for tracking down this issue.

What are the relevant issue numbers?

I did not create any issue and could not find any. So I created the needed MR directly.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated via this MR
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• Security reports checked/validated by reviewer