Warn if Python changes are not rebased (#21016)
Warn if Python changes are not rebased (#21016)

We are introducing this change temporary to make sure that Python
changes will not accidentally introduce new MyPy errors after we
merge them.

This check might be disabled ~week after we enable MyPy as failing
check.
bolkedebruin/airflow,Acehaidrey/incubator-airflow,lyft/incubator-airflow,apache/airflow,apache/airflow,cfei18/incubator-airflow,apache/airflow,danielvdende/incubator-airflow,danielvdende/incubator-airflow,cfei18/incubator-airflow,cfei18/incubator-airflow,danielvdende/incubator-airflow,Acehaidrey/incubator-airflow,bolkedebruin/airflow,nathanielvarona/airflow,bolkedebruin/airflow,bolkedebruin/airflow,nathanielvarona/airflow,cfei18/incubator-airflow,Acehaidrey/incubator-airflow,danielvdende/incubator-airflow,Acehaidrey/incubator-airflow,danielvdende/incubator-airflow,apache/airflow,nathanielvarona/airflow,Acehaidrey/incubator-airflow,lyft/incubator-airflow,lyft/incubator-airflow,apache/airflow,nathanielvarona/airflow,apache/airflow,Acehaidrey/incubator-airflow,nathanielvarona/airflow,nathanielvarona/airflow,bolkedebruin/airflow,cfei18/incubator-airflow,cfei18/incubator-airflow,lyft/incubator-airflow,danielvdende/incubator-airflow