This changeset fixes several problems with the github actions build. It
removes the dependency on a repo script to install msbuild + VS. It
switches the shell back to cmd.exe, so that the scripts in build.yml
continue to run. It installs nuget via chocolatey, since that's not on
the path by default. Finally, it also uses built in MSBUILD to satisfy
the first statement.
This tests out the github actions system, which is quite weird and undocumented. It says this only works with .NET core by default but also supports "4.5.1" as a version. It also says we aren't in the right github actions beta, so this shouldn't work at all.
Since we don't have any developers with GitHub sponsorships turned on, and we don't currently accept donations, this enables the sponsor button so people can donate money to very poor people.
