Update CHANGELOG.md for 12.9.0

[ci skip]

changelogs/unreleased/207249-prevent-editing-weight-to-scroll-to-the-top.yml

----
-title: Prevent editing weight to scroll to the top.
-merge_request: 26613
-author: Gilang Gumilar
-type: fixed

changelogs/unreleased/207367-change-link-icons-on-security-configuration-page-to-follow-design-.yml

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-title: Resolve Change link-icons on security configuration page to follow design system
-merge_request: 26340
-author:
-type: other

changelogs/unreleased/207390-pages-api-case-insensitive-domain-lookup.yml

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-title: 'Add index on LOWER(domain) for pages_domains'
-merge_request: 25664
-author:
-type: other

changelogs/unreleased/207455-frontend-fix-epic-blform.yml

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-title: Fix "Add an epic" form
-merge_request: 26003
-author:
-type: fixed

changelogs/unreleased/207462-scoped-labels-rendering-is-broken-in-todos.yml

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-title: Fix scoped labels rendering in To-Do List
-merge_request: 26146
-author:
-type: fixed

changelogs/unreleased/207464-prevent-unauthorized-user-to-lock-an-issue-when-the-sidebar-is-col.yml

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-title: Prevent unauthorized users to lock an issue from the collapsed sidebar.
-merge_request: 26324
-author: Gilang Gumilar
-type: fixed

changelogs/unreleased/207468-note-confidential-attribute.yml

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-title: Add confidential attribute to notes table
-merge_request:
-author:
-type: other

changelogs/unreleased/207536-retried-jobs-are-not-able-to-find-knapsack-report.yml

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-title: Keep needs association on the retried build
-merge_request: 25888
-author:
-type: fixed

changelogs/unreleased/207623-fix-code-search-pagination.yml

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-title: Fix code search pagination on a custom branch
-merge_request: 25984
-author:
-type: fixed

changelogs/unreleased/207808-geo-bug-filedownloaddispatchworker-may-sometimes-excessively-resyn.yml

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-title: 'Use uncached SQL queries for Geo long-running workers'
-merge_request: 26187
-author:
-type: fixed

changelogs/unreleased/207927-validate-actor-user-against-codeowners.yml

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-title: Validate actor against CODEOWNERS entries
-merge_request:
-author:
-type: fixed

changelogs/unreleased/207962-deploy-ecs.yml

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-title: Add CI template to deploy to ECS
-merge_request: 26371
-author:
-type: added

changelogs/unreleased/207976-stop-markdown-caching-of-non-markdown-snippet-content.yml

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-title: Fix Snippet content incorrectly caching
-merge_request: 25985
-author:
-type: fixed

changelogs/unreleased/208128-add-external-pull-request-to-existing-object-relations.yml

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-title: Fix ImportFailure when restore ci_pipelines:external_pull_request relation
-merge_request: 26041
-author:
-type: fixed

changelogs/unreleased/208151-code-review-analytics-shows-no-data-for-mrs-in-review-for-less-tha.yml

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-title: 'Code Review Analytics: Fix review time display'
-merge_request: 26057
-author:
-type: fixed

changelogs/unreleased/208153-add-anchor-to-related-issues-and-related-merge-requests.yml

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-title: Add anchor tags to related issues and related merge requests.
-merge_request: 26756
-author: Gilang Gumilar
-type: added

changelogs/unreleased/208167-bigfix-unable-to-fork-project-to-the-same-namespace.yml

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-title: Allow to fork to the same namespace and different path via API call
-merge_request: 26062
-author:
-type: fixed

changelogs/unreleased/208242-scoped-label-rendering-in-emails-is-broken.yml

----
-title: Fix scoped labels rendering in emails
-merge_request: 26347
-author:
-type: fixed

changelogs/unreleased/208258-update-documentation-and-common_metrics-yml-to-match-new-y_axis-pr.yml

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-title: Update charts documentation and common_metrics.yml to enable data formatting
-merge_request: 26048
-author:
-type: added

changelogs/unreleased/208403-attachment-file-not-found.yml

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-title: Ensure valid mount point is used by attachments on notes
-merge_request: 26849
-author:
-type: fixed