Remove upper limit on python version

[DominikPeters]

No description provided.

[CLAassistant]

All committers have signed the CLA.

[tkralphs]

I'll merge this as soon as tests pass. I guess that CI is waiting on the CLA being signed? It's a trivial change so a CLA is probably not technically needed, but it's not easy to bypass it.

[tkralphs]

I could also probably just create a duplicate PR myself.

[DominikPeters]

Hi, sorry I forgot about this, I just signed the CLA.

[tkralphs]

I'm probably missing something obvious, but I'm not sure why the CI is not running here.

[tkralphs]

Well, there are a lot of failures, but they mostly seem to be related to problems with the Highs interface, not due to the PR, so I will just go ahead and merge this. It would be great if someone could address some of these failures in another PR.

[rschwarz]

It would be great if someone could address some of these failures in another PR.

We did fix some bugs in the HiGHS interface, but the PR (#405) didn't get any attention back then, so we have added further changes to a fork at https://github.com/Doing-The-Math/python-mip.

I could create another PR with all of these, but it would be worth reviewing them, as well.