Today I've tried to repro dotnet/roslyn#59240 using older SDKs to see when the issue was introduced to Roslyn.

I was not able to run the benchmarks for netcoreapp3.1 and net5.0.

The fixes belong to two categories:

• installer channel mapping: I've just used latest versions available at https://github.com/dotnet/installer
• using older C# syntax as the 3.1 SDK failed to compile the benchmarks. I know it ain't pretty, but I think it's still valuable to be able to run the benchmarks for 3.1. 3.1 EOL is December 3, 2022 so it's just one more year with old C# syntax ;) (source)