Backport "Fix Self Hosted Duo Beta features not being available" to 18.0

What does this MR do and why?

This MR backports the bug fix from MR !190817 (merged) that resolves GitLab Duo Self-hosted beta features not being available in version 18.0. The original fix was merged right after the 18.0 cutoff (commit 1465f38a) and is working correctly in 18.1. This backport is needed to unblock multiple high-opportunity customer POVs that depend on GitLab Duo Self-hosted beta features.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• This MR is backporting a bug fix, documentation update, or spec fix, previously merged in the default branch.
• The MR that fixed the bug on the default branch has been deployed to GitLab.com (not applicable for documentation or spec changes).
• This MR has a severity label assigned (if applicable).
• Set the milestone of the merge request to match the target backport branch version.
• This MR has been approved by a maintainer (only one approval is required).
• Ensure the e2e:test-on-omnibus-ee job has either succeeded or been approved by a Software Engineer in Test.

Note to the merge request author and maintainer

If you have questions about the patch release process, please:

• Refer to the patch release runbook for engineers and maintainers for guidance.
• Ask questions on the #releases Slack channel (internal only).