The entity_created data producer expects $entity->getCreatedTime() to be an int, but is is a string

Thanks, that is surprising! Can you add a test case? Looks like test coverage was missing before, but we should ensure the code is tested.

I do not think, that test coverage is missing, the tests just mock the getCreatedTime() method to return an integer value. This might even be correct for Postgres, not sure. To test this we would need to have functional test with a real database connection.
But I also could just change the existing test to return a string.

Ah ok, I don't think we need a functional test, we can just use a real entity. Can you create a node in the test and use that instead of a mock? We have a database connection available in our kernel tests.