mercure.hub.default.publisher is deprecated

When loading the test data, these deprecation messages appear:

[02-Nov-2021 19:49:20 UTC] 2021-11-02T19:49:20+00:00 [info] User Deprecated: Since symfony/mercure-bundle 0.2: The "mercure.hub.default.publisher" service is deprecated. You should stop using it, as it will be removed in the future, use "mercure.hub.default" instead.

I think we need to use HubInterface where we used PublisherInterface before.