Fix security harness script

What does this MR do?

Fix security harness script that prevents users from pushing to dev remote.

The script was not being executed on ubuntu because of incompatible syntax:

git push origin any-security-branch
.git/hooks/pre-push: 10: .git/hooks/pre-push: [[: not found
Counting objects: 4, done.
Delta compression using up to 4 threads.
Compressing objects: 100% (4/4), done.
Writing objects: 100% (4/4), 414 bytes | 414.00 KiB/s, done.
Total 4 (delta 3), reused 0 (delta 0)

This same fix has been applied on Gitlab-CE: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/25050