Updating openstack-cluster-api-controllers-container image to be consistent with ART for 4.21

Reconciling with https://github.com/openshift/ocp-build-data/tree/5c68d71385f72cd67a199bc4590068053a833c7d/images/openstack-cluster-api-controllers.yml

Author: AOS Automation Release Team

.ci-operator.yaml

@@ -1,4 +1,4 @@
 build_root_image:
   name: release
   namespace: openshift
-  tag: rhel-9-release-golang-1.24-openshift-4.20
+  tag: rhel-9-release-golang-1.24-openshift-4.21

Dockerfile.rhel

@@ -13,7 +13,7 @@
 # limitations under the License.
 
 # Build the manager binary
-FROM registry.ci.openshift.org/ocp/builder:rhel-9-golang-1.24-openshift-4.20 AS builder
+FROM registry.ci.openshift.org/ocp/builder:rhel-9-golang-1.24-openshift-4.21 AS builder
 WORKDIR /workspace
 
 # Run this with docker build --build_arg goproxy=$(go env GOPROXY) to override the goproxy
@@ -38,7 +38,7 @@ RUN CGO_ENABLED=0 GOOS=linux GOARCH=${ARCH} \
     -o manager
 
 # Production image
-FROM registry.ci.openshift.org/ocp/4.20:base-rhel9
+FROM registry.ci.openshift.org/ocp/4.21:base-rhel9
 WORKDIR /
 COPY --from=builder /workspace/manager .
 COPY --from=builder /workspace/infracluster-controller .