Improve messy handling of default connection in K8S hook tests

[amoghrajesh]

Related to #52137

Error: https://github.com/apache/airflow/actions/runs/15846391568/job/44669878466?pr=52129

___________ TestKubernetesHook.test_missing_default_connection_is_ok ___________
providers/cncf/kubernetes/tests/unit/cncf/kubernetes/hooks/test_kubernetes.py:443: in test_missing_default_connection_is_ok
    BaseHook.get_connection(DEFAULT_CONN_ID)
E   Failed: DID NOT RAISE <class 'airflow.exceptions.AirflowNotFoundException'>

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[amoghrajesh]

Wont work independently, added as a commit in #52129 instead