fix setting task nodes class names (#18607)
fix setting task nodes class names (#18607)

The stroke colour and tooltips were not set
correctly for some tasks (depending on the ordering of `g.nodes`).
bolkedebruin/airflow,cfei18/incubator-airflow,Acehaidrey/incubator-airflow,danielvdende/incubator-airflow,danielvdende/incubator-airflow,apache/airflow,Acehaidrey/incubator-airflow,lyft/incubator-airflow,danielvdende/incubator-airflow,Acehaidrey/incubator-airflow,cfei18/incubator-airflow,bolkedebruin/airflow,Acehaidrey/incubator-airflow,nathanielvarona/airflow,danielvdende/incubator-airflow,lyft/incubator-airflow,Acehaidrey/incubator-airflow,cfei18/incubator-airflow,danielvdende/incubator-airflow,lyft/incubator-airflow,bolkedebruin/airflow,nathanielvarona/airflow,bolkedebruin/airflow,apache/airflow,Acehaidrey/incubator-airflow,danielvdende/incubator-airflow,apache/incubator-airflow,mistercrunch/airflow,mistercrunch/airflow,apache/incubator-airflow,cfei18/incubator-airflow,bolkedebruin/airflow,apache/incubator-airflow,cfei18/incubator-airflow,apache/airflow,nathanielvarona/airflow,apache/airflow,nathanielvarona/airflow,apache/airflow,mistercrunch/airflow,nathanielvarona/airflow,nathanielvarona/airflow,apache/incubator-airflow,apache/airflow,mistercrunch/airflow,cfei18/incubator-airflow,lyft/incubator-airflow