[Airflow-4136] Fix overwrite of key_file by constructor (#5155)
[Airflow-4136] Fix overwrite of key_file by constructor (#5155)

This fix the overwrite of the constructor which sets the key_file to None even if user specified otherwise.
Acehaidrey/incubator-airflow,Fokko/incubator-airflow,mtagle/airflow,sekikn/incubator-airflow,wileeam/airflow,spektom/incubator-airflow,r39132/airflow,danielvdende/incubator-airflow,lyft/incubator-airflow,dhuang/incubator-airflow,Acehaidrey/incubator-airflow,Fokko/incubator-airflow,dhuang/incubator-airflow,nathanielvarona/airflow,apache/airflow,nathanielvarona/airflow,DinoCow/airflow,nathanielvarona/airflow,airbnb/airflow,bolkedebruin/airflow,mrkm4ntr/incubator-airflow,nathanielvarona/airflow,airbnb/airflow,mtagle/airflow,cfei18/incubator-airflow,r39132/airflow,mrkm4ntr/incubator-airflow,danielvdende/incubator-airflow,lyft/incubator-airflow,apache/incubator-airflow,dhuang/incubator-airflow,nathanielvarona/airflow,apache/airflow,wileeam/airflow,apache/incubator-airflow,Acehaidrey/incubator-airflow,bolkedebruin/airflow,apache/airflow,cfei18/incubator-airflow,apache/airflow,Acehaidrey/incubator-airflow,mistercrunch/airflow,cfei18/incubator-airflow,Fokko/incubator-airflow,wooga/airflow,spektom/incubator-airflow,r39132/airflow,apache/incubator-airflow,mrkm4ntr/incubator-airflow,wooga/airflow,Fokko/incubator-airflow,airbnb/airflow,mtagle/airflow,bolkedebruin/airflow,sekikn/incubator-airflow,r39132/airflow,cfei18/incubator-airflow,mistercrunch/airflow,wooga/airflow,bolkedebruin/airflow,danielvdende/incubator-airflow,mistercrunch/airflow,bolkedebruin/airflow,danielvdende/incubator-airflow,lyft/incubator-airflow,DinoCow/airflow,spektom/incubator-airflow,mrkm4ntr/incubator-airflow,airbnb/airflow,apache/airflow,dhuang/incubator-airflow,lyft/incubator-airflow,wooga/airflow,sekikn/incubator-airflow,DinoCow/airflow,spektom/incubator-airflow,sekikn/incubator-airflow,Acehaidrey/incubator-airflow,cfei18/incubator-airflow,danielvdende/incubator-airflow,cfei18/incubator-airflow,mtagle/airflow,apache/incubator-airflow,mistercrunch/airflow,apache/airflow,DinoCow/airflow,wileeam/airflow,danielvdende/incubator-airflow,Acehaidrey/incubator-airflow,wileeam/airflow,nathanielvarona/airflow