Test that CODEOWNERS reflects docs metadata changes
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Capturing @eread's comment in https://gitlab.com/gitlab-org/gitlab/-/merge_requests/135408#note_1625396002 so it's not lost:
> _Ideally we'd have a CI/CD job that would break if an update is done to metadata but not to \[CODEOWNERS]._
Not sure if it's possible, but capturing it just in case.
## Related items
- Related to https://gitlab.com/gitlab-org/gitlab/-/merge_requests/135408+ where the idea was voiced
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