Use build_id instead, which is guaranteed to be an int

Change-Id: I2737d35b865fdd0dbc3dd4f97c4622ba91995b3e
Reviewed-on: https://flutter-review.googlesource.com/c/recipes/+/46042
Reviewed-by: Godofredo Contreras <godofredoc@google.com>
Commit-Queue: Drew Roen <drewroen@google.com>
(cherry picked from commit fd48758226137a663c91821f39d7c40aeaa0f43f)
Reviewed-on: https://flutter-review.googlesource.com/c/recipes/+/46100
diff --git a/recipes/engine_v2/engine_v2.py b/recipes/engine_v2/engine_v2.py
index d00aa02..7c71a27 100644
--- a/recipes/engine_v2/engine_v2.py
+++ b/recipes/engine_v2/engine_v2.py
@@ -184,7 +184,7 @@
   if not_experimental and dart_internal_build:
     api.pubsub.publish_message(
         BUILD_RESULT_PUBSUB_ENDPOINT,
-        json.dumps({"buildbucket_id": api.buildbucket.build.id}),
+        json.dumps({"buildbucket_id": api.buildbucket.build_id}),
         step_name='Publish build results'
     )