I wrote a GitHub Action to select an MSVC version

Alright, I’m not breaking new ground here, but this is a difficulty I’ve had, and maybe it’s a difficulty you’ve had too. It’s not common, but if you want to compile your code with a particular version of MSVC, it’s already fairly finicky on your own machine. It’s even worse with GitHub Actions, where you have no UI. Before sitting down this week to figure it out, I’ve never had success with…