Update CHANGELOG.md for 8.16.0

changelogs/unreleased/25701-standardize-text-colors.yml

...ed/25705-your-commands-have-been-executed-is-overkill.yml

changelogs/unreleased/25725-remove-window-object.yml

changelogs/unreleased/25776-alerts-should-be-responsive.yml

...-update-username-button-remains-disabled-upon-failure.yml

changelogs/unreleased/25898-ci-icon-color-mr.yml

...ed/25941-odd-overflow-behavior-for-long-issue-headers.yml

...logs/unreleased/25946-manual-pipeline-dropdown-casing.yml

...eased/25985-combine-members-and-groups-settings-pages.yml

...996-Move-award-emoji-out-of-the-discussion-tab-for-MR.yml

changelogs/unreleased/26014-fix-update-doc.yml

...gs/unreleased/26051-fix-missing-endpoint-route-method.yml

...released/26109-preserve-scroll-position-on-autoreload.yml

changelogs/unreleased/26129-add-link-to-branches-page.yml

.../26134-ctrl-enter-does-not-submit-a-new-merge-request.yml

...e-request-tabs-don-t-render-when-no-commits-available.yml

changelogs/unreleased/26192-fixes-too-short-input.yml

changelogs/unreleased/26207-add-hover-animations.yml

...erate-all-haml-fixtures-within-teaspoon-fixtures-task.yml

changelogs/unreleased/26238-buttons-not-accessible.yml