Build a fixture that can return right response based on input msg for sdk comms

### Body Reference: https://github.com/apache/airflow/pull/54083#discussion_r2253896206 TLDR: Right now we kind of hardcode the responses a comms object should return almost blindly. We could have a fixture that rightly detects the kind of request and responds accordingly. ### Committer - [x] I acknowledge that I am a maintainer/committer of the Apache Airflow project.