Improve CI by testing generated addon's directly in CI not as nested test in Tox

[MrTango]

Motivation

right now it is not easy to find the breaking test message if a test inside a generated addon breaks.
If we generate the addon package in the CI directly and run the tox inside that package, we should be able to read it better, because there will be no nesting.

Risks

We might lose this functionally in local env or we have two ways how we run test inside generated packages.
Alternatively we have to find a way how to flatten this in tox.

[MrTango]

@gforcada @mauritsvanrees ideas are very welcome ;)