Update gateway.mdx

Author: JoanCamosTyk

developer-support/release-notes/gateway.mdx

@@ -3718,7 +3718,13 @@ If you are upgrading to 5.3.13, please follow the detailed [upgrade instructions
 #### Changelog
 <a id="Changelog-v5.3.13"></a>
 
-No changes in this release.
+##### Fixed
+
+<AccordionGroup>
+<Accordion title='Updated Gateway TLS Certificate'>
+Renewed the self-signed certificate shipped in gateway Docker images with extended validity until March 2029. The updated certificate now uses Subject Alternative Names (SAN) instead of the deprecated Common Name (CN) field, ensuring compatibility with modern TLS standards and Go 1.17+. This change affects deployments using `global.tls.gateway=true` in Helm configurations. No action required, existing deployments will automatically use the new certificate on upgrade.
+</Accordion>
+</AccordionGroup>
 
 ### 5.3.12 Release Notes