Set build tree permissions in tests run as root
    
    GitLab CI tends to place files owned by less privileged users
    from DIFFERENT jobs in the repository checkout in the show_highstate
    job which runs as root, which then fails Git calls at the safe.directory
    test.
    Albeit not understanding this, mitigate it by recursively setting
    the permissions in the build environment of tests executed as root.
    
    Signed-off-by: Georg Pfuetzenreuter <mail@georg-pfuetzenreuter.net>