[AIRFLOW-5100] Respect safe_mode configuration setting when parsing DAG files (#5757)
[AIRFLOW-5100] Respect safe_mode configuration setting when parsing DAG files (#5757)

The scheduler calls `list_py_file_paths` to find DAGs to schedule. It does so
without passing any parameters other than the directory. This means that
it *won't* discover DAGs that are missing the words "airflow" and "DAG" even
if DAG_DISCOVERY_SAFE_MODE is disabled.

Since `list_py_file_paths` will refer to the configuration if
`include_examples` is not provided, it makes sense to have the same behaviour
for `safe_mode`.

airbnb/airflow,mistercrunch/airflow,wileeam/airflow,bolkedebruin/airflow,lyft/incubator-airflow,apache/airflow,apache/airflow,Acehaidrey/incubator-airflow,wooga/airflow,mistercrunch/airflow,Fokko/incubator-airflow,Acehaidrey/incubator-airflow,airbnb/airflow,danielvdende/incubator-airflow,cfei18/incubator-airflow,mrkm4ntr/incubator-airflow,mistercrunch/airflow,mrkm4ntr/incubator-airflow,sekikn/incubator-airflow,sekikn/incubator-airflow,sekikn/incubator-airflow,danielvdende/incubator-airflow,DinoCow/airflow,bolkedebruin/airflow,spektom/incubator-airflow,airbnb/airflow,airbnb/airflow,spektom/incubator-airflow,dhuang/incubator-airflow,dhuang/incubator-airflow,nathanielvarona/airflow,danielvdende/incubator-airflow,apache/incubator-airflow,cfei18/incubator-airflow,cfei18/incubator-airflow,wileeam/airflow,danielvdende/incubator-airflow,Acehaidrey/incubator-airflow,apache/incubator-airflow,lyft/incubator-airflow,wooga/airflow,nathanielvarona/airflow,bolkedebruin/airflow,wooga/airflow,apache/airflow,sekikn/incubator-airflow,cfei18/incubator-airflow,apache/airflow,mrkm4ntr/incubator-airflow,cfei18/incubator-airflow,DinoCow/airflow,DinoCow/airflow,nathanielvarona/airflow,bolkedebruin/airflow,nathanielvarona/airflow,mtagle/airflow,lyft/incubator-airflow,mtagle/airflow,mrkm4ntr/incubator-airflow,wooga/airflow,wileeam/airflow,bolkedebruin/airflow,DinoCow/airflow,apache/airflow,apache/incubator-airflow,spektom/incubator-airflow,mistercrunch/airflow,wileeam/airflow,apache/incubator-airflow,Acehaidrey/incubator-airflow,dhuang/incubator-airflow,apache/airflow,Fokko/incubator-airflow,Acehaidrey/incubator-airflow,nathanielvarona/airflow,danielvdende/incubator-airflow,lyft/incubator-airflow,Acehaidrey/incubator-airflow,cfei18/incubator-airflow,nathanielvarona/airflow,mtagle/airflow,Fokko/incubator-airflow,danielvdende/incubator-airflow,dhuang/incubator-airflow,mtagle/airflow,Fokko/incubator-airflow,spektom/incubator-airflow