Ignore error msg if namespace exists

docs/installation/install_oas.rst

@@ -150,7 +150,7 @@ directory **on your provisioning machine**. Don't forget to replace
    export KUBECONFIG=$CLUSTER_DIR/kube_config_cluster.yml
 
    # Ensure flux-system namespace is created
-   kubectl get namespace flux-system || kubectl create namespace flux-system
+   kubectl get namespace flux-system 2>/dev/null || kubectl create namespace flux-system
 
    # This inserts the configuration from .flux.env into your cluster as a "secret"
    kubectl apply -k $CLUSTER_DIR