Update Istio to 1.7.3

Author: github-actions[bot]

istio/operator/manifests.yaml

@@ -247,7 +247,7 @@ spec:
       serviceAccountName: istio-operator
       containers:
         - name: istio-operator
-          image: docker.io/istio/operator:1.7.2
+          image: docker.io/istio/operator:1.7.3
           command:
           - operator
           - server