Rename variable `serialize_dag` to `serialized_dag` (#19265)
Rename variable `serialize_dag` to `serialized_dag` (#19265)

The expression `serialize_dag` represents an action, but the variable is actually a dag that has been _serialized_.
apache/incubator-airflow,nathanielvarona/airflow,danielvdende/incubator-airflow,cfei18/incubator-airflow,cfei18/incubator-airflow,Acehaidrey/incubator-airflow,Acehaidrey/incubator-airflow,mistercrunch/airflow,mistercrunch/airflow,bolkedebruin/airflow,Acehaidrey/incubator-airflow,mistercrunch/airflow,bolkedebruin/airflow,apache/airflow,apache/airflow,apache/incubator-airflow,nathanielvarona/airflow,Acehaidrey/incubator-airflow,danielvdende/incubator-airflow,apache/incubator-airflow,danielvdende/incubator-airflow,cfei18/incubator-airflow,nathanielvarona/airflow,lyft/incubator-airflow,cfei18/incubator-airflow,lyft/incubator-airflow,danielvdende/incubator-airflow,bolkedebruin/airflow,danielvdende/incubator-airflow,lyft/incubator-airflow,danielvdende/incubator-airflow,bolkedebruin/airflow,bolkedebruin/airflow,Acehaidrey/incubator-airflow,nathanielvarona/airflow,lyft/incubator-airflow,mistercrunch/airflow,apache/airflow,apache/airflow,nathanielvarona/airflow,apache/incubator-airflow,Acehaidrey/incubator-airflow,apache/airflow,nathanielvarona/airflow,cfei18/incubator-airflow,cfei18/incubator-airflow,apache/airflow