fix: Allow absolute paths in securefile download command

Swapnaneel Patrarequested to merge
gitlab-community/gitlab-org/cli:8081 into main

Description

Fixes glab securefile download --path /tmp/test error "path escapes from parent" by detecting absolute paths and bypassing os.Root restrictions for them.

Related Issues

Resolves #8081

How has this been tested?

All 18 existing unit tests pass

Relative path traversal protection still works

Screenshots (if appropriate):

Edited by Swapnaneel Patra

Merge request reports