Fix AirflowSkipException message raised by KubernetesPodOperator

[dolfinus]

• KubernetesPodOperator.skip_on_exit_code is always a container (like list[int]), it cannot be None.
• If pod exited with matching exit code, AirflowSkipException should contain exact exit code instead of container value.
• Allow to pass KubernetesPodOperator(skip_no_exit_code=0) to skip successfully finished pods. Previously it was the same as KubernetesPodOperator(skip_no_exit_code=[])

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[hussein-awala]

It looks good

[hussein-awala]

I checked the recent changes, and they look good. Waiting for a second approval before merging.

[romsharon98]

Looks good!