Update net-contour nightly (#12542)
Update net-contour nightly (#12542)

bumping knative.dev/net-contour a971f5d...a248e38:
  > a248e38 Update community files (# 711)
  > 169ded4 drop dead/unused symlink (# 706)
  > d5cb481 upgrade to latest dependencies (# 710)

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