Update CHANGELOG.md for 12.8.0

[ci skip]

changelogs/unreleased/24020-copy-markdown-from-comments.yml

----
-title: Fix copy markdown with elements with no text content
-merge_request: 24020
-author:
-type: fixed

changelogs/unreleased/24108-fix-sast-multiline.yml

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-title: Fix multiline issue when loading env vars from DinD in SAST
-merge_request: 24108
-author:
-type: fixed

changelogs/unreleased/24415-restrict-wiki-page-titles.yml

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-title: Limit length of wiki file/directory names
-merge_request: 24364
-author:
-type: changed

changelogs/unreleased/24779-super-group-milestone-view-doesn-t-include-milestones-from-projects.yml

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-title: Include milestones from subgroups in the list of Group Milestones.
-merge_request: 22922
-author:
-type: fixed

changelogs/unreleased/24992-add-avatar_url-and-email_user-in_web_hook.yml

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-title: add avatar_url in job webhook, and email in pipeline webhook
-merge_request: 24992
-author: Guillaume Micouin
-type: added

changelogs/unreleased/25276-allow-forward-deploys-only.yml

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-title: Allow to deploy only forward deployments
-merge_request: 22959
-author:
-type: changed

changelogs/unreleased/25970-mirror-pull-for-archived-projects.yml

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-title: Disable pull mirror importing for archived projects
-merge_request: 24029
-author:
-type: fixed

changelogs/unreleased/26113-webide-upload-encoding.yml

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-title: Fix some of the file encoding issues when uploading in the Web IDE
-merge_request: 23761
-author:
-type: fixed

changelogs/unreleased/26247-junit-xml-tests-mis-present-the-test-execution-time-from-test-cases.yml

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-title: Label MR test modal execution time as seconds
-merge_request: 24019
-author:
-type: fixed

changelogs/unreleased/28352-group-issues-api-searches-archived-projects.yml

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-title: Add non_archived param to issues API endpoint to filter issues from archived projects
-merge_request: 23785
-author:
-type: added

changelogs/unreleased/28352-group-merge-request-api-searches-archived-projects.yml

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-title: Add non_archived param to group merge requests API endpoint to filter MRs from non archived projects
-merge_request: 23809
-author:
-type: added

changelogs/unreleased/28376-merge-request-comments-have-stopped-appearing-for-the-whole-project.yml

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-title: Fix Merge Request comments when some notes are corrupt
-merge_request: 23786
-author:
-type: fixed

changelogs/unreleased/28872-admin-area-s-account-and-limit-fields-could-be-improved.yml

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-title: Add clarifying content to account fields
-merge_request:
-author:
-type: other

changelogs/unreleased/28965-fix-filter-hover-state.yml

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-title: Add border radius and remove blue outline on recent searches filter
-merge_request: 23266
-author:
-type: fixed

changelogs/unreleased/29077-remove-two_step_rebase-feature-flag.yml

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-title: Update rebasing to use the new two-phase Gitaly Rebase RPC
-merge_request: 23546
-author:
-type: changed

changelogs/unreleased/29984-asynchronous-mr-mergeability-check.yml

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-title: Check mergeability of MR asynchronously
-merge_request: 21026
-author:
-type: performance

changelogs/unreleased/29987-revert-groups-overview-font-spacing-to-the-old-more-space-efficient.yml

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-title: Reducing whitespace in group list to show more on screen and reduce vertical scrolling
-merge_request: 21584
-author:
-type: other

changelogs/unreleased/30235-support-allow-failure-for-ci-rules.yml

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-title: Implement support of allow_failure keyword for CI rules
-merge_request: 24605
-author:
-type: added

changelogs/unreleased/30631-allow-empty-needs-v4.yml

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-title: Implement allowing empty needs for jobs in DAG pipelines
-merge_request: 22246
-author:
-type: added

changelogs/unreleased/31034-upgrade-to-rails-6.yml

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-title: Upgrade to Rails 6
-merge_request: 19891
-author:
-type: other