Test package building against upstream conda, conda-build, and conda-smithy

It would be great to run builds with a few select feedstocks against various upstream infrastructure. For example we could try to build some feedstocks against upstream conda pulled from [conda-canary](https://anaconda.org/conda-canary/conda) and from rc tags of conda-build/smithy. This may allow us to troubleshoot issues before they hit us in the face.