Update istio/operator Docker tag to v1.7.6

hardening_manifest.yaml

@@ -27,7 +27,7 @@ labels:
   org.opencontainers.image.url: "https://istio.io/"
   ## Name of the distributing entity, organization or individual
   org.opencontainers.image.vendor: "opensource"
-  org.opencontainers.image.version: "1.7.5"
+  org.opencontainers.image.version: "1.7.6"
   ## Keywords to help with search (ex. "cicd,gitops,golang")
   mil.dso.ironbank.image.keywords: "istio"
   ## This value can be "opensource" or "commercial"