[AIRFLOW-6969] Move backport build to test (#7603)
[AIRFLOW-6969] Move backport build to test (#7603)

When one of the test builds fails even restarting it does not help to succeed
the whole job if there is "post-test" stage. The post-test job will remain in
cancelled state after the job is restarted

We should move prepare-backport-packages to test phase (it is very fast).
danielvdende/incubator-airflow,Acehaidrey/incubator-airflow,danielvdende/incubator-airflow,Acehaidrey/incubator-airflow,mistercrunch/airflow,apache/incubator-airflow,nathanielvarona/airflow,mrkm4ntr/incubator-airflow,apache/airflow,DinoCow/airflow,cfei18/incubator-airflow,wooga/airflow,bolkedebruin/airflow,apache/incubator-airflow,bolkedebruin/airflow,wooga/airflow,Acehaidrey/incubator-airflow,Acehaidrey/incubator-airflow,wooga/airflow,apache/airflow,airbnb/airflow,danielvdende/incubator-airflow,bolkedebruin/airflow,nathanielvarona/airflow,bolkedebruin/airflow,sekikn/incubator-airflow,apache/airflow,airbnb/airflow,dhuang/incubator-airflow,sekikn/incubator-airflow,apache/incubator-airflow,Acehaidrey/incubator-airflow,DinoCow/airflow,danielvdende/incubator-airflow,apache/airflow,dhuang/incubator-airflow,sekikn/incubator-airflow,apache/airflow,dhuang/incubator-airflow,DinoCow/airflow,DinoCow/airflow,mrkm4ntr/incubator-airflow,wooga/airflow,cfei18/incubator-airflow,lyft/incubator-airflow,apache/incubator-airflow,mistercrunch/airflow,lyft/incubator-airflow,nathanielvarona/airflow,airbnb/airflow,danielvdende/incubator-airflow,nathanielvarona/airflow,cfei18/incubator-airflow,lyft/incubator-airflow,nathanielvarona/airflow,mrkm4ntr/incubator-airflow,danielvdende/incubator-airflow,cfei18/incubator-airflow,nathanielvarona/airflow,bolkedebruin/airflow,apache/airflow,sekikn/incubator-airflow,cfei18/incubator-airflow,airbnb/airflow,mistercrunch/airflow,lyft/incubator-airflow,dhuang/incubator-airflow,mrkm4ntr/incubator-airflow,mistercrunch/airflow,Acehaidrey/incubator-airflow,cfei18/incubator-airflow