Add branch name check to security-harness script
## Description The security fix must be done in the branch that name starts with `security`, such as: `security-rs-milestone-xss-12-6` since these branches cannot be pushed to the canonical repositories on `gitlab.com/gitlab-org`. This helps ensure security merge requests don't get leaked prematurely [docs](https://gitlab.com/gitlab-org/release/docs/blob/master/general/security/engineer.md#security-merge-requests). ## Solution Update the [`security-harness`](https://gitlab.com/gitlab-org/gitlab/-/blob/master/scripts/security-harness) script to verify that the branch has `security-` prefix.
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