[Infrastructure] Make sure the SDK tests run against an up to date version of the ASP.NET Core runtime

https://github.com/dotnet/sdk/blob/a30e465a2e2ea4e2550f319a2dc088daaafe5649/Directory.Build.targets#L42-L46

The tests in the SDK will use the correct runtime version, however they won't do the same for ASP.NET Core. This causes issues where things that break the SDK go unnoticed until ASP.NET Core needs to consume a new SDK version, at which point is blocked from doing so because of the incompatibility that wasn't caught.