Disable pipeline must succeed setting for security policy project

What does this MR do and why?

This change fixes a bug with security policy project when Pipeline must succeed setting is enabled for the group the project belongs to. This setting should be overriden to false for security policy project as it does not have CI/CD enabled and no pipeline runs for the MRs.

This MR fixes it by overriding only_allow_merge_if_pipeline_succeeds for the security policy project.

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

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Before	After

How to set up and validate locally

• Create a group/sub-group and enable Pipeline must succeed setting from Settings->Merge requests
• Create a security policy for the group/sub-group and verify that the security policy project is created
• Verify that MR created for the new policy can be merged and does not block due to missing pipeline.

Addresses #478084 (closed)