[Automated] Update net-contour nightly

[knative-automation]

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

Produced via:

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

Details:

bumping knative.dev/net-contour fa98465...c73a318:
  > c73a318 upgrade to latest dependencies (# 1258)