Fix Non-DB test collection failure in Google Stackdriver hook test

[FrankYang0529]

The CI in #68625 failed with following message:

ERROR providers/google/tests/unit/google/cloud/hooks/test_stackdriver.py - sqlalchemy.exc.InvalidRequestError: When initializing mapper Mapper[AssetWatcherModel(asset_watcher)], expression 'Trigger' failed to locate a name ('Trigger'). If this is a class name, consider adding this relationship() to the <class 'airflow.models.asset.AssetWatcherModel'> class after both dependent classes have been defined.

https://github.com/apache/airflow/actions/runs/36953939813/job/110675454131?pr=68625

Why

• test_stackdriver.py passes Connection(conn_id="google_cloud_default") as the return_value of a mock.patch decorator. That expression runs when pytest imports the module during collection. Creating the ORM object makes SQLAlchemy configure every mapper that is registered at that moment.
• No test setup imports all models before collection. For a PR that only changes the kafka provider, selective checks run only the apache.kafka, common.compat, common.messaging and google tests. The kafka asset tests import the airflow.models.asset module through common.compat. That module defines AssetWatcherModel, which has a relationship to Trigger. No test module has imported airflow.models.trigger yet when test_stackdriver.py is collected.

How

• Change it to mock.MagicMock(spec=Connection).

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Was generative AI tooling used to co-author this PR?

• Yes - Claude Code

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