Test 04 (deep dag): Issues with multiprocessing

[Nix3c3r]

Hi I have problems to get test_04_deep_dag() running correctly.
When running as is, it results into an AttributeError. The error message states problems with local objects, which is common for multiprocessing:
AttributeError: Can't pickle local object 'DagTestCase.test_04_deep_dag.<locals>.run_test'
The line it fails is:

django-postgresql-dag/tests/test.py

Line 625 in 20c4797

p.start()

I'm running this from Windows. As far as I know Windows systems have pickle-issues. Maybe there is an alternative to using multiprocessing? One can also not use signal, as this is missing some functionality on Windows.

[JackAtOmenApps]

@Nix3c3r Thank you for pointing this out. I need to add some better CI for this repo to check for these sorts of issues, and will see about how I can resolve this. I've added this to my to-do list.