Merge branch 'docs-update-review-app-group' into 'master'

Update group for review apps

See merge request gitlab-org/gitlab!74156

doc/ci/review_apps/index.md

 ---
-stage: Release
-group: Release
+stage: Verify
+group: Testing
 info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#assignments
 type: reference
 ---