[CI] Docs should be built when config.yml is changed (#13710)
[CI] Docs should be built when config.yml is changed (#13710)

The "Build Docs" job was not running when the config.yml file changed, example: https://github.com/apache/airflow/pull/13709

It should run it as Configuration Reference page (https://airflow.apache.org/docs/apache-airflow/2.0.0/configurations-ref.html) is built using that file
cfei18/incubator-airflow,lyft/incubator-airflow,apache/airflow,Acehaidrey/incubator-airflow,mistercrunch/airflow,nathanielvarona/airflow,lyft/incubator-airflow,lyft/incubator-airflow,sekikn/incubator-airflow,cfei18/incubator-airflow,bolkedebruin/airflow,mistercrunch/airflow,apache/incubator-airflow,cfei18/incubator-airflow,apache/incubator-airflow,danielvdende/incubator-airflow,nathanielvarona/airflow,danielvdende/incubator-airflow,Acehaidrey/incubator-airflow,sekikn/incubator-airflow,apache/airflow,apache/airflow,apache/airflow,nathanielvarona/airflow,bolkedebruin/airflow,bolkedebruin/airflow,dhuang/incubator-airflow,Acehaidrey/incubator-airflow,sekikn/incubator-airflow,Acehaidrey/incubator-airflow,cfei18/incubator-airflow,apache/incubator-airflow,dhuang/incubator-airflow,danielvdende/incubator-airflow,apache/airflow,apache/airflow,danielvdende/incubator-airflow,dhuang/incubator-airflow,cfei18/incubator-airflow,nathanielvarona/airflow,lyft/incubator-airflow,bolkedebruin/airflow,danielvdende/incubator-airflow,nathanielvarona/airflow,mistercrunch/airflow,apache/incubator-airflow,Acehaidrey/incubator-airflow,mistercrunch/airflow,nathanielvarona/airflow,sekikn/incubator-airflow,dhuang/incubator-airflow,bolkedebruin/airflow,Acehaidrey/incubator-airflow,danielvdende/incubator-airflow,cfei18/incubator-airflow