Update IronBank base image to 9.6 (elastic#131302) (elastic#132207)

(cherry picked from commit 067a812)

Author: brianseeders

distribution/docker/src/docker/iron_bank/hardening_manifest.yaml

@@ -11,7 +11,7 @@ tags:
 # Build args passed to Dockerfile ARGs
 args:
   BASE_IMAGE: "redhat/ubi/ubi9"
-  BASE_TAG: "9.5"
+  BASE_TAG: "9.6"
 # Docker image labels
 labels:
   org.opencontainers.image.title: "elasticsearch"