[Wasm] Proxy crashes due to CEL using thread unsafe protobuf interface

https://prow.istio.io/view/gs/istio-prow/pr-logs/pull/istio_istio/28170/integ-pilot-k8s-tests_istio/22361

Seems very often, likely a regression