setting Envoy update branch to 1.36 for Istio 1.28 (#5758)

* setting Envoy update branch to 1.36 for Istio 1.28

* missing make gen

Author: grnmeira

prow/cluster/jobs/istio/proxy/istio.proxy.release-1.28.gen.yaml

@@ -1466,7 +1466,7 @@ jobs:
   - --labels=auto-merge
   - --modifier=update_envoy_dep
   - --token-env
-  - --cmd=UPDATE_BRANCH=main scripts/update_envoy.sh
+  - --cmd=UPDATE_BRANCH=release/v1.36 scripts/update_envoy.sh
   env:
   - name: BUILD_WITH_CONTAINER
     value: "0"