Update CHANGELOG.md for 12.9.0

[ci skip]

changelogs/unreleased/36243-introduce-an-optional-expiration-date-for-ssh-keys.yml

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-title: Introduce optional expiry date for SSH Keys
-merge_request: 26351
-author:
-type: added

changelogs/unreleased/37256-bump-wh-version.yml

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-title: Enable Workhorse upload acceleration for Project Import uploads via API
-merge_request: 26914
-author:
-type: performance

changelogs/unreleased/37256-use-workhorse-acceleration-on-project-import.yml

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-title: Enable Workhorse upload acceleration for Project Import API
-merge_request: 25361
-author:
-type: performance

changelogs/unreleased/37320-ensure-project-snippet-api-status.yml

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-title: Project Snippets API endpoints check feature status
-merge_request: 26064
-author:
-type: performance

changelogs/unreleased/37320-ensure-project-snippet-feature-status-in-project-snippet-api-endpoi.yml

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-title: Project Snippets GraphQL resolver checks feature status
-merge_request: 26158
-author:
-type: performance

changelogs/unreleased/37951-project-settings-required-approval-input-not-sequential-order.yml

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-title: Fix project setting approval input in non-sequential order
-merge_request: 25391
-author:
-type: fixed

changelogs/unreleased/38096-splitmr-write-resource-milestone-events-pd.yml

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-title: Add possibility to track milestone changes on issues and merge requests
-merge_request: 24780
-author:
-type: added

changelogs/unreleased/38143-replace-labels-in-vue-with-gitlab-ui-component.yml

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-title: Update labels in Vue with GlLabel component
-merge_request: 21465
-author:
-type: changed

changelogs/unreleased/38144-replace-labels-in-haml-with-gitlab-ui-css.yml

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-title: New styles for scoped labels
-merge_request: 21377
-author:
-type: changed

changelogs/unreleased/38145-replace-labels-in-non-vue-js-with-gitlab-ui-component.yml

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-title: Correctly style scoped labels in sidebar after updating
-merge_request: 22071
-author:
-type: changed

changelogs/unreleased/38414.yml

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-title: Fix error details layout and alignment for mobile view
-merge_request: 24390
-author:
-type: fixed

changelogs/unreleased/40585-token-disclaimer.yml

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-title: Improvement in token reference
-merge_request:
-author:
-type: other

changelogs/unreleased/55487-backfill-lfs-objects-projects.yml

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-title: Backfill LfsObjectsProject records of forks
-merge_request: 26964
-author:
-type: other

changelogs/unreleased/63-nudge-users-to-select-a-template-to-set-up-a-pipeline.yml

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-title: Nudge users to select a gitlab-ci.yml template
-merge_request: 24622
-author:
-type: added

changelogs/unreleased/7003-fail-to-start-server-without-ar-connection.yml

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-title: Refuse to start web server without a working ActiveRecord connection
-merge_request: 25160
-author:
-type: other

changelogs/unreleased/7583-developer-cannot-push-to-projects-they-create-in-groups.yml

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-title: Introduce default branch protection at the group level
-merge_request: 24426
-author:
-type: added

changelogs/unreleased/Remove-refreshData-function-logic-from-issue-js.yml

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-title: Moves refreshData from issue model to board store
-merge_request: 21409
-author: nuwe1
-type: other

changelogs/unreleased/Resolve-Migrate--fa-spinner-app-assets-javascripts-notes-components-discu.yml

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-title: Migrate .fa-spinner to .spinner for app/assets/javascripts/notes/components/discussion_resolve_button.vue
-merge_request: 25055
-author: nuwe1
-type: other

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

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-title: Remove spinner from app/views/award_emoji
-merge_request: 25032
-author: nuwe1
-type: other

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

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-title: Migrate .fa-spinner to .spinner for app/views/help
-merge_request: 25037
-author: nuwe1
-type: other