Backport of PR #2029 to bareos-23

Checklist for the reviewer of the PR (will be processed by the Bareos team)

Make sure you check/merge the PR using devtools/pr-tool to have some simple automated checks run and a proper changelog record added.

General

• Correct milestone is set

Source code quality (if there were changes to the original PR)

• Source code changes are understandable
• Variable and function names are meaningful
• Code comments are correct (logically and spelling)
• Required documentation changes are present and part of the PR

Backport quality

• Original PR dedupable device: fix example files #2029 is merged
• All functional differences to the original PR are documented above