Fix script typo in secret detection template causing detection to be skipped

What does this MR do?

Fixes #297475 (closed)

To address a script typo in the Secrets-Detection CI template from !51129 (merged):

Instead of:

if [[ $CI_COMMIT_TAG ]]; then ...; exit 0; fi

the template contained:

if [[ $CI_COMMIT_TAG ]]; ...; then exit 0; fi

(the then was in the wrong place, causing pipelines to skip detection in both cases where CI_COMMIT_TAG is defined and where CI_COMMIT_TAG is not defined)

Screenshots (strongly suggested)

• .gitlab-ci.yml: https://gitlab.com/zrice/secrets/-/blob/master/.gitlab-ci.yml
• QA demo: https://gitlab.com/zrice/secrets/-/jobs/961659703 job passing. Before this was showing "Skipping job because CI_COMMIT_TAG is set".

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• [-] Label as security and @ mention @gitlab-com/gl-security/appsec
• [-] The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• [-] Security reports checked/validated by a reviewer from the AppSec team