Add EKS 1.28 to extended support

Author: jdewinne

docs/vendor/testing-supported-clusters.md

@@ -314,7 +314,7 @@ Compatibility Matrix supports creating [AWS EKS](https://aws.amazon.com/eks/?nc2
   </tr>
   <tr>
     <th>Supported Kubernetes Versions</th>
-    <td><p>1.28, 1.29, 1.30, 1.31</p><p>Extended Support Versions: 1.24, 1.25, 1.26, 1.27</p></td>
+    <td><p>1.29, 1.30, 1.31</p><p>Extended Support Versions: 1.24, 1.25, 1.26, 1.27, 1.28</p></td>
   </tr>
   <tr>
     <th>Supported Instance Types</th>