Update CHANGELOG.md for 12.6.0

[ci skip]

changelogs/unreleased/31914-graphql-mark-all-todos-as-done-pd.yml

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-title: Add GraphQL mutation to mark all todos done for a user
-merge_request: 19482
-author:
-type: added

changelogs/unreleased/31914-graphql-todo-query-support-multiple-query.yml

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-title: Enable support for multiple content query in GraphQL Todo API
-merge_request: 19576
-author:
-type: changed

changelogs/unreleased/31914-graphql-todo-restore-pd.yml

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-title: Add GraphQL mutation to restore a Todo
-merge_request: 20261
-author:
-type: added

changelogs/unreleased/32115-structured-logging-mail_room.yml

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-title: Upgrade `mail_room` gem to 0.10.0 and enable structured logging
-merge_request: 19186
-author:
-type: added

changelogs/unreleased/32358-add-modsec-blocking-usage-stats-per-project.yml

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-title: Add modsecurity deployment counts to usage ping
-merge_request: 20196
-author:
-type: added

changelogs/unreleased/32470-ui-degradation-on-environment-folder-view.yml

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-title: Fix broken UI on Environment folder
-merge_request: 17427
-author: Takuya Noguchi
-type: fixed

changelogs/unreleased/32557-convert-generic-epic-error-banners-to-form-validation-messages.yml

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-title: Convert flash epic error to form validation error
-merge_request: 20130
-author:
-type: changed

changelogs/unreleased/32557-fix-error-adding-already-linked-issue.yml

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-title: Fix error when linking already linked issue to epic
-merge_request: 21213
-author:
-type: fixed

changelogs/unreleased/32778-change-retries-approach-promql-queries.yml

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-title: Improve the way the metrics dashboard waits for data
-merge_request: 20687
-author:
-type: fixed

changelogs/unreleased/32780-when-zooming-metrics-at-some-point-we-can-t-adjust-the-zoom-any-fur.yml

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-title: Fixed monitor charts from throwing error when zoomed
-merge_request: 20331
-author:
-type: fixed

changelogs/unreleased/32897-convert-alerts-to-toasts.yml

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-title: Convert flash alerts to toasts
-merge_request: 20356
-author:
-type: added

changelogs/unreleased/32959-dismissal-ux-improvement.yml

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-title: Improve UX for vulnerability dismissal note
-merge_request: 20768
-author:
-type: fixed

changelogs/unreleased/33052-design-comment-link-styling.yml

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-title: Add link color to design comments
-merge_request: 20302
-author:
-type: fixed

changelogs/unreleased/33099-add-pipelines-api-order-by-updated-at.yml

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-title: Allow order_by updated_at in Pipelines API
-merge_request: 19886
-author:
-type: added

changelogs/unreleased/33099-updated_at-filters-for-pipelines-api.yml

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-title: Add updated_before and updated_after filters to the Pipelines API endpoint
-merge_request: 21133
-author:
-type: added

changelogs/unreleased/33257-prevent-accidental-deletions-via-soft-delete-for-groups-services.yml

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-title: Add services for 'soft-delete for groups' feature
-merge_request: 19358
-author:
-type: added

changelogs/unreleased/33257-prevent-accidental-deletions-via-soft-delete-for-groups-workers.yml

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-title: Add workers for 'soft-delete for groups' feature
-merge_request: 19679
-author:
-type: added

changelogs/unreleased/33318-make-internal-projects-poolable.yml

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-title: Make internal projects poolable
-merge_request: 19295
-author: briankabiro
-type: changed

changelogs/unreleased/33338-notify-user-if-they-have-over-1000-epics-in-roadmap.yml

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-title: Notify user when over 1000 epics in roadmap
-merge_request: 19419
-author:
-type: added

changelogs/unreleased/33482-allow-text-wrapping-on-repository-tags-page.yml

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-title: Allow patch notes on repo tags page to word wrap
-merge_request: 20135
-author:
-type: fixed