GeezerVison

@MattKiazyk I don't have enough context to judge where else could this be extended, but I think it could be a good idea to make the decoding a bit more resilient when depending on external models.

My thinking is that the downloadable runtimes that can be decoded successfully should still be available even if some runtimes fail to decode.
A bit of context on why I arrived to this conclusion:

• We are using xcodes in our CI pipeline to download earlier iOS runtimes
• Looking at the latest plist, those runtimes weren't affected by the unhandled added enum case

Feel free to close and ignore this if you don't think it's appropriate.

I also thought about failing the Authentication decoding to nil, but I am not sure if that's the appropriate way as nil authentication might have some semantic meaning as opposed to an unhandled case.