Reinstate ipyparallel downstream tests

[ianthomas23]

With the merging of ipython/ipyparallel#947 into the ipyparallelmain branch,, we can re-enable the downstream ipyparallel tests here.

[ianthomas23]

Evidently there are more failures that need investigating.

[minrk]

I just got the ipyparallel CI back into a healthy state, so I can look into this now.

[minrk]

@ianthomas23 all I had to do was make a 9.0.2 release with your ipython/ipyparallel#947 and all is well, sorry it took so long. The combination of main + main is also tested on the ipyparallel repo and passing, too.

[ianthomas23]

Thanks @minrk!