Decrease likelihood of memory issue in CI (#18852)
Decrease likelihood of memory issue in CI (#18852)

This PR attempts to decrease the likelihood of memory issues for
CI for non-committers. The MSSQL and MYSQL Provider and Integration
tests when run together with other tests in parallel (for MSSQL even
standalone) might cause memory problems (143 or 137 exit code).

This PR changes the approach slightly for low-memory conditions:

1) MSSQL - both Integration and Providers tests are skipped
   entirely (they will be run in High-Mem case so we will see if
   there are any problems anyway)

2) MySQL - both Integration and Providers tests are run separately
   which will lead to slightly longer test runs but likely this
   will save us from the occasional memory issues.
mistercrunch/airflow,nathanielvarona/airflow,Acehaidrey/incubator-airflow,danielvdende/incubator-airflow,lyft/incubator-airflow,apache/airflow,apache/airflow,lyft/incubator-airflow,cfei18/incubator-airflow,danielvdende/incubator-airflow,apache/incubator-airflow,bolkedebruin/airflow,cfei18/incubator-airflow,cfei18/incubator-airflow,nathanielvarona/airflow,mistercrunch/airflow,mistercrunch/airflow,danielvdende/incubator-airflow,bolkedebruin/airflow,nathanielvarona/airflow,nathanielvarona/airflow,cfei18/incubator-airflow,bolkedebruin/airflow,bolkedebruin/airflow,lyft/incubator-airflow,danielvdende/incubator-airflow,cfei18/incubator-airflow,nathanielvarona/airflow,Acehaidrey/incubator-airflow,apache/incubator-airflow,apache/airflow,Acehaidrey/incubator-airflow,Acehaidrey/incubator-airflow,danielvdende/incubator-airflow,mistercrunch/airflow,danielvdende/incubator-airflow,apache/airflow,lyft/incubator-airflow,apache/airflow,apache/airflow,apache/incubator-airflow,Acehaidrey/incubator-airflow,apache/incubator-airflow,bolkedebruin/airflow,cfei18/incubator-airflow,Acehaidrey/incubator-airflow,nathanielvarona/airflow