Enhance the system to be able to run test differing in NullHandling more natually

### Motivation

Right now the CI runs the [tests twice](https://github.com/apache/druid/blob/master/.github/workflows/reusable-unit-tests.yml#L89-L93); differing only in the setting of this flag.

I have faced it several times that I was testing with value X and with Y it failed; regardless that I've run the test from the commandline as I was not setting the flag...

### Description

I think any option would be interesting which could possibly run both versions of the test during the same maven execution.

Start with the two test runs in .github/workflows/reusable-unit-tests.yml at lines 89-93 and trace how the NullHandling flag is passed during Maven and command-line execution. Determine whether both flag variants can run in one Maven execution, then verify that the relevant tests execute under each setting.

Written by the indexing model from the issue text.