[Automated] Update backstage-plugins-eventing nightly (#304)

Update eventing nightly

bumping knative.dev/eventing 903c74c...2bd6d6a:
  > 2bd6d6a Fix MT Channel based broker when OIDC is enabled (# 8727)
  > ffe3a4b Use PullIfNotPresent pull policy for auth-proxy image (# 8735)

Signed-off-by: Knative Automation <automation@knative.team>

Author: knative-automation