Fix sqlalchemy warning about coercing subquery for use in IN() (#22788)
Fix sqlalchemy warning about coercing subquery for use in IN() (#22788)

On task log, when using postgres db, you would see a warning:

WARNING - /usr/local/lib/python3.7/site-packages/sqlalchemy/sql/coercions.py:521
SAWarning: Coercing Subquery object into a select() for use in IN();
please pass a select() construct explicitly

This PR fixes it
apache/airflow,Acehaidrey/incubator-airflow,apache/airflow,nathanielvarona/airflow,lyft/incubator-airflow,danielvdende/incubator-airflow,nathanielvarona/airflow,cfei18/incubator-airflow,nathanielvarona/airflow,danielvdende/incubator-airflow,apache/airflow,nathanielvarona/airflow,cfei18/incubator-airflow,lyft/incubator-airflow,apache/airflow,cfei18/incubator-airflow,apache/airflow,Acehaidrey/incubator-airflow,danielvdende/incubator-airflow,Acehaidrey/incubator-airflow,danielvdende/incubator-airflow,nathanielvarona/airflow,cfei18/incubator-airflow,nathanielvarona/airflow,danielvdende/incubator-airflow,lyft/incubator-airflow,danielvdende/incubator-airflow,Acehaidrey/incubator-airflow,Acehaidrey/incubator-airflow,lyft/incubator-airflow,apache/airflow,cfei18/incubator-airflow,Acehaidrey/incubator-airflow,cfei18/incubator-airflow