Update fixtures for AI stage/group changes

From Draft to Ready

• gitlab-com/www-gitlab-com!127858 (merged) is merged
• We pull the data for the fixture files again, but this time from the main page (I took them from https://ai-powered-stage.about.gitlab-review.app for this MR)
  • https://about.gitlab.com/sections.json
  • https://about.gitlab.com/stages.json
  • https://about.gitlab.com/groups.json
  • https://about.gitlab.com/categories.json

Context

Follow-up of #1375 (closed)

What does this MR do and why?

• Updates fixtures with data taken from the review-app in gitlab-com/www-gitlab-com!127858 (merged).
• Rename ~"group::ai assisted" to ~group::ai model validation in the codebase
• Regenerated policies
• Fixed specs

Expected impact & dry-runs

N/A

Action items

• If adding environment variables for reactive processors, update config/triage-web.yaml and .gitlab/ci/triage-web.yml
• (If applicable) Add documentation to the handbook pages for Triage Operations =>
• (If applicable) Identify the affected groups and how to communicate to them:
  • /cc @person_or_group =>
  • Relevant Slack channels =>
  • Engineering week-in-review