Allow failure for Secret Detection job

What does this MR do?

This makes Secret Detection behavior consistent with the other Secure analyzers.

Currently, a failure of the Secret Detection job will cause a pipeline to fail, but this is not the case for our other Secure jobs. With this change, a failure of the Secret Detection job will not cause a pipeline to fail.

Screenshots (strongly suggested)

Current behavior where the Secret Detection job caused the pipeline to fail. The other Secure jobs, gemnasium and license_scanning had the same error, but did not cause the pipeline to fail.

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