Add the new Airflow Trove Classifier to setup.cfg (#22241)
Add the new Airflow Trove Classifier to setup.cfg (#22241)

We have new Trove Classifiers in PyPI for Apache Airflow:

https://github.com/pypa/trove-classifiers/pull/87

This PR adds it for Airflow. The next release of Providers will
add the classifiers for providers.
cfei18/incubator-airflow,Acehaidrey/incubator-airflow,danielvdende/incubator-airflow,apache/airflow,nathanielvarona/airflow,lyft/incubator-airflow,cfei18/incubator-airflow,apache/airflow,nathanielvarona/airflow,apache/airflow,Acehaidrey/incubator-airflow,lyft/incubator-airflow,lyft/incubator-airflow,Acehaidrey/incubator-airflow,Acehaidrey/incubator-airflow,danielvdende/incubator-airflow,cfei18/incubator-airflow,cfei18/incubator-airflow,nathanielvarona/airflow,Acehaidrey/incubator-airflow,apache/airflow,danielvdende/incubator-airflow,Acehaidrey/incubator-airflow,nathanielvarona/airflow,apache/airflow,apache/airflow,cfei18/incubator-airflow,danielvdende/incubator-airflow,danielvdende/incubator-airflow,lyft/incubator-airflow,nathanielvarona/airflow,nathanielvarona/airflow,cfei18/incubator-airflow,danielvdende/incubator-airflow