gitlab-runner-helper: use default umask

scripts/gitlab-runner-helper sets umask to 0000 to fix issues where ci jobs would be running as a different user, preventing access to files.

This causes issues when files in repositories end up in build artifacts with world writable permissions.

One such example is the alpine-gitlab-ci project where /etc/sudoers.d ends up word-writable, preventing sudo to work.

Set it to the standard 0022 to fix this issue.