Avoiding silent failure on pubsub notification.

1) Removing try..except around pubsub notification, which would silently fail on errors.
2) Adding infra_step=True, to designate responsibility.

Bug: 78810
Change-Id: I83a1233025bed35810384b68b2344f6d0155ba67
Reviewed-on: https://flutter-review.googlesource.com/c/recipes/+/11520
Reviewed-by: Keyong Han <keyonghan@google.com>
Commit-Queue: Yusuf Mohsinally <mohsinally@google.com>