Update CHANGELOG.md for 12.8.0

[ci skip]

changelogs/unreleased/expose-more-user-preferences-in-api.yml

----
-title: Expose theme and color scheme user preferences in API
-merge_request: 24409
-author:
-type: changed

changelogs/unreleased/expose_is_using_seat_for_group_members.yml

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-title: Expose is_using_seat attribute for Member in API
-merge_request: 21496
-author:
-type: added

changelogs/unreleased/fe-ide-minor-improvements-for-commit-options.yml

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-title: Minor text update to IDE commit to branch disabled tooltip
-merge_request: 24521
-author:
-type: other

changelogs/unreleased/fe-ide-nav-switch-branches-and-mr-tab-order.yml

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-title: Switch order of tabs in Web IDE nav dropdown
-merge_request: 24199
-author:
-type: changed

changelogs/unreleased/fe-update-empty-state-btn-x-margin.yml

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-title: Update button margin of various empty states
-merge_request: 24806
-author:
-type: other

changelogs/unreleased/feat-backfill-group-graphql-api.yml

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-title: Backfill missing GraphQL API Group type properties
-merge_request: 23389
-author: Fabio Huser
-type: added

changelogs/unreleased/feat-drop-signatures-email-replies.yml

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-title: Drop signatures in email replies
-merge_request: 25389
-author: Diego Louzán
-type: changed

changelogs/unreleased/feat-x509-signed-commits.yml

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-title: x509 signed commits using openssl
-merge_request: 17773
-author: Roger Meier
-type: added

changelogs/unreleased/feature-flag-strategy-scope-tables.yml

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-title: Create operations strategies and scopes tables
-merge_request: 24819
-author:
-type: added

changelogs/unreleased/feature-no-reload-permalink.yml

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-title: When switching to a file permalink, just change the URL instead of triggering
-  a useless page reload
-merge_request: 22340
-author:
-type: added

changelogs/unreleased/feature-set-redis-hard-limits.yml

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-title: Sets size limits on data loaded async, like deploy boards and merge request reports
-merge_request: 21871
-author:
-type: changed

changelogs/unreleased/fix-blocked-status.yml

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-title: Show blocked status for all blocked issues on issue boards
-merge_request: 24631
-author:
-type: fixed

changelogs/unreleased/fix-child-parent-pipeline-for-mr.yml

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-title: Allow running child pipelines as merge request pipelines
-merge_request: 23884
-author:
-type: fixed

changelogs/unreleased/fix-disable-admin-mode-link-in-dashboard.yml

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-title: Fix POST method in dashboard link for disabling admin mode
-merge_request: 23363
-author: Diego Louzán
-type: fixed

changelogs/unreleased/fix-do-not-update-private-profile-in-api.yml

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-title: Fix inconditionally setting user profile to public when updating via
-  API and private_profile parameter is not present in the request
-merge_request: 24456
-author: Diego Louzán
-type: fixed

changelogs/unreleased/fix-duplicated-user-popover.yml

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-title: Fix duplicated user popovers
-merge_request: 24405
-author:
-type: fixed

changelogs/unreleased/fix-ide-pipeline-background.yml

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-title: Fix pipeline icon background in Web IDE
-merge_request: 24707
-author:
-type: fixed

changelogs/unreleased/fix-merge-train-race-condition.yml

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-title: Use state machine in Merge Train to avoid race conditions
-merge_request: 23395
-author:
-type: fixed

changelogs/unreleased/fix-merge-train-to-evaluate-in_progress_merge_commit_sha.yml

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-title: Fix merge train unnecessarily retries pipeline by a race condition
-merge_request: 24566
-author:
-type: fixed

changelogs/unreleased/fix-ms-teams-branch-setting.yml

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-title: Fix missing API notification argument for Microsoft Teams
-merge_request: 23571
-author: Seiji Suenaga
-type: fixed