Add Downstream tests?

[isaacsas]

I guess we should at least add SBMLToolkit once it is considered stable and ReactionNetworkImporters. @paulflang what do you think?

Any other packages that make sense?

[paulflang]

Well, would be nice to see if Catalyst updates break SBMLTk. Even before it is stable. But testing SBMLTk costs some time, so Idk if it should be triggered on every push. In any case, I would not consider SBMLTk stable yet.

[ChrisRackauckas]

Compute is cheap. We should do it.