• create a new key go/flutter-cirrus#create-a-new-key
• update key in
  • flutter/assets-for-api-docs
  • flutter/flutter
  • flutter/engine
  • flutter/packages
  • flutter/plugins
• update plugins GCLOUD_FIREBASE_TESTLAB_KEY following last two items in go/flutter-cirrus#setup

/cc @ricardoamador

Long term fix is to use workload identity federation: #114916