Update CHANGELOG.md for 12.9.0

[ci skip]

changelogs/unreleased/Resolve-Migrate--fa-spinner-app-views-ide.yml

----
-title: Migrate .fa-spinner to .spinner for app/views/ide
-merge_request: 25022
-author: nuwe1
-type: other

changelogs/unreleased/Resolve-Migrate--fa-spinner-app-views-projects-find_file.yml

----
-title: Migrate .fa-spinner to .spinner for app/views/projects/find_file
-merge_request: 25051
-author: nuwe1
-type: other

changelogs/unreleased/Resolve-Migrate--fa-spinner-app-views-projects-forks.yml

----
-title: Remove .fa-spinner from app/views/projects/forks
-merge_request: 25034
-author: nuwe1
-type: other

changelogs/unreleased/Resolve-Migrate--fa-spinner-app-views-projects-notes.yml

----
-title: Remove spinner from app/views/projects/notes
-merge_request: 25015
-author: nuwe1
-type: other

changelogs/unreleased/Resolve-Migrate--fa-spinner-app-views-shared-badges.yml

----
-title: Remove unused loading spinner from badge_settings partial
-merge_request: 25044
-author: nuwe1
-type: other

changelogs/unreleased/Resolve-Migrate--fa-spinner-app-views-snippets-notes.yml

----
-title: Remove .fa-spinner from app/views/snippets/notes
-merge_request: 25036
-author: nuwe1
-type: other

changelogs/unreleased/Resolve-Migrate--fa-spinner-ee-app-views-shared-members.yml

----
-title: Migrate .fa-spinner to .spinner for ee/app/views/shared/members
-merge_request: 25019
-author: nuwe1
-type: other

changelogs/unreleased/a11y-ci-template.yml

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-title: Add accessibility scanning CI template
-merge_request: 25144
-author:
-type: added

changelogs/unreleased/a11y-gitlab-script.yml

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-title: Generate JSON-formatted a11y CI artifacts
-merge_request: 26687
-author:
-type: added

changelogs/unreleased/ac-remove-track_mr_picking-ff.yml

----
-title: Track merge request cherry-picks
-merge_request: 26907
-author:
-type: added

changelogs/unreleased/add-endpoint-to-remove-sidekiq-jobs-based-on-metadata.yml

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-title: Add admin API endpoint to delete Sidekiq jobs matching metadata
-merge_request: 25998
-author:
-type: added

changelogs/unreleased/add-feature-flags-version.yml

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-title: Add version column to operations_feature_flags table
-merge_request: 25552
-author:
-type: added

changelogs/unreleased/add-gatsby.yml

----
-title: Add Project template for Gatsby
-merge_request: 25486
-author:
-type: added

changelogs/unreleased/add-missing-secure-queues-changelog.yml

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-title: Move namespace of Secure Sidekiq queues
-merge_request: 24340
-author:
-type: other

changelogs/unreleased/add-retiresjs-vars-to-dependency-scanning.yml

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-title: Add vars to allow air-gapped usage of Retire.js (Dependency Scanning)
-merge_request: 26463
-author:
-type: added

changelogs/unreleased/add-shard-label-to-queue-timing-histogram-metric.yml

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-title: Add 'shard' label for 'job_queue_duration_seconds' metric
-merge_request: 23536
-author:
-type: changed

changelogs/unreleased/add-sidekiq-metrics-for-gitaly-and-db-time.yml

----
-title: Add Prometheus metrics for Gitaly and database time in background jobs
-merge_request: 26384
-author:
-type: changed

changelogs/unreleased/add-static-object-external-storage-url-to-csp-rules.yml

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-title: Inject CSP values when repository static objects external caching is enabled
-merge_request: 25711
-author:
-type: fixed

changelogs/unreleased/add-trigger-include-artifact.yml

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-title: 'Create child pipelines dynamically using content from artifact as CI configuration'
-merge_request: 23790
-author:
-type: fixed

changelogs/unreleased/add-user-job-title-column.yml

----
-title: Add support for user Job Title
-merge_request: 25483
-author:
-type: added