metainfo: Update release notes for 8.3.0 (#210)

Author: ryonakano

platform-data/data/platform.appdata.xml.in

@@ -16,6 +16,8 @@
         <p>Platform updates:</p>
         <ul>
           <li>Rebase on GNOME 49 runtime</li>
+          <li>Update Granite to 7.7.0</li>
+          <li>Update Icons to 8.2.0</li>
         </ul>
       </description>
     </release>