Codeowners threat insights govern

What does this MR do?

groupthreat insights is now part of the Govern stage

Related to https://gitlab.com/gitlab-org/govern/general/-/issues/759

What are the relevant issue numbers?

Checklist

• Ensure changes can be built upon without requiring a breaking change, see Building for Extensibility.
• Review and add/update tests for this feature/bug.
• Add an entry to the CHANGELOG if required, with the appropriate version. See Classifying Changes.
• Assign the MR to the appropriate person/people for review.