python3-ipyparallel: enable check

[tornaria]

Testing the changes

• I tested the changes in this PR: briefly

[tornaria]

@ahesford I had to disable check on musl since it's broken, both in CI and locally. The cluster just gets stuck (it seems a python process dies but the parent doesn't realize).

The checks pass just fine in x86_64 and i686 (both locally and in all my pushes to gh), so this is better than what was there before.

I'm not looking into it anymore. As a starting point, ipyparallel/tests/test_apps.py::test_ipcluster_start_stop always fails. But then other files sometimes result in all errors (not failures), sometimes they don't (test_asyncresult.py, test_client.py, test_cluster.py, ...).