Merge branch 'otovar/fix-feature-flag-error-message' into 'master'

Fix missing example from valid_usage! error message

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/145330



Merged-by: Rémy Coutable <remy@rymai.me>
Approved-by: Rémy Coutable <remy@rymai.me>
Reviewed-by: Rémy Coutable <remy@rymai.me>
Reviewed-by: Oscar Tovar <otovar@gitlab.com>
Co-authored-by: Oscar Tovar <otovar@gitlab.com>