Fix payload structure for duo_agent_platform_enabled in group settings

What does this MR do and why?

Fixes the payload structure for duo_agent_platform_enabled in group settings to:

{ "ai_settings_attributes": { "duo_agent_platform_enabled": false } }

References

• Relevant BE MR: !216143+

Screenshots or screen recordings

Screen Recording 2025-12-11 at 3.24.20 PM.mov

How to set up and validate locally

• Run GDK on SASS mode: GITLAB_SIMULATE_SAAS=1 gdk start
• Go to group GitLab Duo settings: /groups/gitlab_duo/-/settings/gitlab_duo/configuration
• Toggle the GitLab Duo Agent Platform checkbox and save changes
• Ensure setting is persisted

MR acceptance checklist

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