Update net-istio nightly (#11568)
Update net-istio nightly (#11568)

bumping knative.dev/net-istio 13a2470...ef6c1a6:
  > ef6c1a6 upgrade to latest dependencies (# 684)

Signed-off-by: Knative Automation <f415700d4d0ce1c81810fe7553e3eea2bed16231@knative.team>
knative/serving,knative/serving