Fix doublestar implementation to use paths relative to working directory
What does this MR do?
Fixes an issue encountered in retrieving artifacts with absolute paths: gitlab#388334 (comment 1243400143)
Why was this MR needed?
To fix the issue.
What's the best way to test this MR?
CI passing, as well as running @stanhu's test case: gitlab#388334 (comment 1243279596)