Bump CI image (RL9 only)

Author: priteau

environments/.stackhpc/tofu/cluster_image.auto.tfvars.json

@@ -1,6 +1,6 @@
 {
     "cluster_image": {
         "RL8": "openhpc-RL8-250820-0800-767addd8",
-        "RL9": "openhpc-RL9-250820-0800-767addd8"
+        "RL9": "openhpc-RL9-250908-2047-d90ebd0e"
     }
 }