[Automated] Update net-istio nightly

[knative-automation]

/assign @knative/serving-writers
/cc @knative/serving-writers

Produced via:

for x in net-istio.yaml; do
  curl https://storage.googleapis.com/knative-nightly/net-istio/latest/$x > ${GITHUB_WORKSPACE}/./third_party/istio-latest/$x
done

Details:

bumping knative.dev/net-istio bc04895...9647beb:
  > 9647beb Update actions (# 1322)

[knative-prow]

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