[Workers] Add changelog entry for V8 sandbox (#24535)

Author: fhanau

src/content/release-notes/workers.yaml

@@ -3,6 +3,9 @@ link: "/workers/platform/changelog/"
 productName: Workers
 productLink: "/workers/"
 entries:
+  - publish_date: "2025-08-14"
+    description: |-
+      - Enable V8 Sandbox for improved isolation and security.
   - publish_date: "2025-08-11"
     description: |-
       - The MessageChannel and MessagePort APIs are now available in Workers.