Fix swapped descriptions for refactor/tests in Duo Chat doc

What does this MR do and why?

During the GitLab Duo Coffee Chat at Summit 2024, we discussed Chat features and scopes. We spotted that the description for refactoring and tests is swapped. https://docs.gitlab.com/ee/user/gitlab_duo_chat.html

This MR fixes the descriptions.

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.

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

Before	After

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.