Fix failing docs build on Master (#11951)
Fix failing docs build on Master (#11951)

This was merged in #11472, but for some reason that didn't run tests so
the failure wasn't noticed.

a7ad204 fixed 1 error but the docs error was missed
cfei18/incubator-airflow,cfei18/incubator-airflow,nathanielvarona/airflow,bolkedebruin/airflow,DinoCow/airflow,bolkedebruin/airflow,danielvdende/incubator-airflow,cfei18/incubator-airflow,nathanielvarona/airflow,apache/incubator-airflow,mrkm4ntr/incubator-airflow,DinoCow/airflow,bolkedebruin/airflow,Acehaidrey/incubator-airflow,lyft/incubator-airflow,airbnb/airflow,bolkedebruin/airflow,sekikn/incubator-airflow,DinoCow/airflow,Acehaidrey/incubator-airflow,lyft/incubator-airflow,dhuang/incubator-airflow,airbnb/airflow,mistercrunch/airflow,mistercrunch/airflow,cfei18/incubator-airflow,mistercrunch/airflow,nathanielvarona/airflow,mrkm4ntr/incubator-airflow,nathanielvarona/airflow,dhuang/incubator-airflow,sekikn/incubator-airflow,apache/incubator-airflow,apache/airflow,apache/incubator-airflow,danielvdende/incubator-airflow,bolkedebruin/airflow,lyft/incubator-airflow,cfei18/incubator-airflow,danielvdende/incubator-airflow,mistercrunch/airflow,danielvdende/incubator-airflow,apache/airflow,apache/airflow,nathanielvarona/airflow,Acehaidrey/incubator-airflow,dhuang/incubator-airflow,sekikn/incubator-airflow,airbnb/airflow,airbnb/airflow,Acehaidrey/incubator-airflow,apache/airflow,danielvdende/incubator-airflow,apache/airflow,apache/incubator-airflow,dhuang/incubator-airflow,apache/airflow,mrkm4ntr/incubator-airflow,nathanielvarona/airflow,sekikn/incubator-airflow,Acehaidrey/incubator-airflow,lyft/incubator-airflow,DinoCow/airflow,cfei18/incubator-airflow,mrkm4ntr/incubator-airflow,danielvdende/incubator-airflow,Acehaidrey/incubator-airflow