Add pre-upgrade feature note and errata to GHES 3.21.2 release notes (#62002)

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Author: pallsama

data/release-notes/enterprise-server/3-21/2.yml

@@ -1,5 +1,8 @@
 date: '2026-06-30'
 sections:
+  features:
+    - |
+      You can now run the pre-upgrade stage of an upgrade outside the maintenance window using `ghe-upgrade --phase pre-upgrade -y UPGRADE-PACKAGE-FILENAME`. Running the pre-upgrade stage in advance can reduce in-maintenance upgrade time by up to 20 minutes. For more information, see [AUTOTITLE](/admin/administering-your-instance/administering-your-instance-from-the-command-line/command-line-utilities#ghe-upgrade). Additional functionality and documentation will be available when you upgrade to 3.22 and later versions.
   security_fixes:
     - |
       **HIGH**: Current configurations of the GitHub API access controls could allow an attacker to create issues in any public repository via a u2s token without requiring the underlying installation to have issues write permission. This therefore allows an attacker to impersonate the victim in public repositories by creating issues and commit comments.
@@ -86,3 +89,6 @@ sections:
       On instances with multiple Git storage nodes in a voting configuration, including cluster and geo-replication high availability topologies, upgrading may fail to correctly install Actions that ship with the new version. In some cases, previous versions of these Actions remain on the instance. To resolve this issue, run the following commands on the primary node: `ghe-config --unset 'app.actions.actions-repos-sha1sum'`, `ghe-config-apply`, and `/usr/local/share/enterprise/ghe-run-init-actions-graph`.
     - |
       Users attempting to clone repositories via HTTPS receive an "Internal Server Error" message, and the clone operation fails with a 500 error. This issue affects all deployment topologies including cluster, standalone, high availability, and geo-replication configurations.
+  errata:
+    - |
+      A note about running the pre-upgrade stage outside the maintenance window has been added to the release notes. [Updated: 2026-06-30]