chore: upgrade redhat docker image to ubi 9.6 (#601)

Signed-off-by: Nic <qianyong@api7.ai>
diff --git a/redhat/Dockerfile b/redhat/Dockerfile
index 8508e7d..8de8b26 100644
--- a/redhat/Dockerfile
+++ b/redhat/Dockerfile
@@ -15,7 +15,7 @@
 # limitations under the License.
 #
 
-FROM registry.access.redhat.com/ubi8/ubi:8.6
+FROM registry.access.redhat.com/ubi9/ubi:9.6
 
 ARG APISIX_VERSION=3.13.0
 LABEL apisix_version="${APISIX_VERSION}"