Remove duplicated WORKDIR in CI Dockerfile (#14697)
Remove duplicated WORKDIR in CI Dockerfile (#14697)

Having it doesn't cause any harm, but it was already set five commands
further up to the same value
mistercrunch/airflow,nathanielvarona/airflow,dhuang/incubator-airflow,apache/airflow,lyft/incubator-airflow,nathanielvarona/airflow,cfei18/incubator-airflow,danielvdende/incubator-airflow,sekikn/incubator-airflow,sekikn/incubator-airflow,Acehaidrey/incubator-airflow,dhuang/incubator-airflow,danielvdende/incubator-airflow,sekikn/incubator-airflow,Acehaidrey/incubator-airflow,bolkedebruin/airflow,danielvdende/incubator-airflow,apache/incubator-airflow,danielvdende/incubator-airflow,nathanielvarona/airflow,cfei18/incubator-airflow,Acehaidrey/incubator-airflow,apache/airflow,lyft/incubator-airflow,bolkedebruin/airflow,Acehaidrey/incubator-airflow,danielvdende/incubator-airflow,sekikn/incubator-airflow,dhuang/incubator-airflow,apache/incubator-airflow,bolkedebruin/airflow,apache/airflow,mistercrunch/airflow,apache/incubator-airflow,apache/airflow,nathanielvarona/airflow,mistercrunch/airflow,cfei18/incubator-airflow,nathanielvarona/airflow,lyft/incubator-airflow,Acehaidrey/incubator-airflow,apache/incubator-airflow,cfei18/incubator-airflow,apache/airflow,cfei18/incubator-airflow,apache/airflow,bolkedebruin/airflow,dhuang/incubator-airflow,danielvdende/incubator-airflow,bolkedebruin/airflow,Acehaidrey/incubator-airflow,cfei18/incubator-airflow,mistercrunch/airflow,lyft/incubator-airflow,nathanielvarona/airflow