message: Get Unreal Engine from GCS instead of S3.
  But still using the AWS CLI via Google interop.
diff: if [ ! -d "/c/Program Files/Epic Games/UE_4.26" ]
  then
  - aws s3 cp s3://cesium-unreal-engine/2021-03-16/UE_4.26.zip .
  + AWS_ACCESS_KEY_ID=${GOOGLE_ACCESS_KEY_ID} AWS_SECRET_ACCESS_KEY=${GOOGLE_SECRET_ACCESS_KEY} aws s3 --endpoint-url https://storage.googleapis.com cp s3://cesium-unreal-engine/2021-03-16/UE_4.26.zip .
  7z x UE_4.26.zip "-oC:\Program Files\Epic Games"
  rm UE_4.26.zip
  - aws s3 cp s3://cesium-unreal-engine/2021-03-16/Launcher.zip .
  + AWS_ACCESS_KEY_ID=${GOOGLE_ACCESS_KEY_ID} AWS_SECRET_ACCESS_KEY=${GOOGLE_SECRET_ACCESS_KEY} aws s3 --endpoint-url https://storage.googleapis.com cp s3://cesium-unreal-engine/2021-03-16/Launcher.zip .
  7z x Launcher.zip "-oC:\Program Files (x86)\Epic Games"
  rm Launcher.zip
  fi
  