Update Framework for Test Project

[pvoelker]

Any objections if I put a pull request out there to update the test project framework? Visual Studio is a bit cranky about .NET Core 2.0.

I can bump up to .NET Core 3.1 or take it all the way up to .NET 7 if we want to... Thoughts?

I'm looking to use this to build a standard interface library for some low cost quiz box hardware....

[benedekkupper]

sure go ahead :) can you send me two commits, one bumping to the lowest still useful version, the second to the most current one?