tests: Fix import error for c23 module

[MrKevinWeiss]

For some strange reason, it seems like using

from module_a import module_b
from module_b import module_c

will not work... I guess any from imports must be an existing module and cannot be something brought in. Note in this example module_b is usable just not "from" importable.

We have had some failing tests which I was able to reproduce locally.

In this case it is regarding the mock -> python2 and unittest.mock -> python3 abstraction.

One can use or print the imported mock, but cannot from x import y it.

The solution is to just import all the from x import y within the version abstraction branch.

It has been locally tested allowing mock to still be used.

The failure was discovered during RIOT release tests

[MrKevinWeiss]

I found some more info on it:

• https://stackoverflow.com/questions/27830262/python-import-function-from-an-already-imported-module