Fix BaseAsyncOperator in common-compat provider for Airflow 2.x

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Fix BaseAsyncOperator in common-compat provider for Airflow 2.x as reported by @kacpermuda

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Hello @kaxil , @kacpermuda found an issue with the backward compat baseoperator due to my PR which add's support for async callable in PythonOperator. This PR is a fix for that issue. Good catch BTW by @kacpermuda. Question, don't we run backward compat tests of providers with Airflow 2.x? I would have expected this to have failed tests.