docs: Update changelog for Zulip Server 9.1 release.

docs/overview/changelog.md

@@ -19,6 +19,34 @@ _Unreleased_
 
 ## Zulip Server 9.x series
 
+### Zulip Server 9.1
+
+_Released 2024-08-02_
+
+- Clarified upgrade notes and installer error messages. Improved
+  documentation to smooth the process of upgrading Ubuntu 20.04 to
+  22.04 before upgrading to Zulip 9.x. Installations currently running
+  Ubuntu 20.04 should first upgrade to the latest Zulip 8.x release,
+  and then follow the [Zulip host OS upgrade
+  instructions](../production/upgrade.md#upgrading-the-operating-system)
+  in preparation for upgrading to Zulip 9.x.
+- Improved web and mobile app loading times and bandwidth usage by
+  tuning API response compression and removing some unnecessary
+  entropy in user object payloads.
+- Fixed how Zulip handles a GitHub quirk, to avoid duplicate
+  notifications when pull request reviews are submitted.
+- Fixed a rare race condition that could cause uploaded images to be
+  displayed as a perpetual loading spinner.
+- Fixed video player controls appearing in the lightbox bottom
+  carousel.
+- Fix several minor visual bugs, most notably with composebox
+  typeahead overflowing incorrectly.
+- Fixed a subtle live-update bug rerendering the inbox view.
+- Fixed a couple of subtle performance issues involving the analytics
+  cron job and listing invitations in organization settings.
+- Updated documentation for a couple of integrations.
+- Updated translations.
+
 ### Zulip Server 9.0
 
 _Released 2024-07-25_

version.py

@@ -14,7 +14,7 @@ ZULIP_VERSION = lines.pop(0).strip()
 ZULIP_MERGE_BASE = lines.pop(0).strip()
 
 LATEST_MAJOR_VERSION = "9.0"
-LATEST_RELEASE_VERSION = "9.0"
+LATEST_RELEASE_VERSION = "9.1"
 LATEST_RELEASE_ANNOUNCEMENT = "https://blog.zulip.com/2023/12/15/zulip-8-0-released/"
 
 # Versions of the desktop app below DESKTOP_MINIMUM_VERSION will be