[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 b6af942...a9517c7:
  > a9517c7 upgrade to latest dependencies (# 1367)

[knative-prow]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: knative-automation
Once this PR has been reviewed and has the lgtm label, please assign dsimansk for approval. For more information see the Kubernetes Code Review Process.

The full list of commands accepted by this bot can be found here.

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment