Matrix build to run unit tests on all supported .NET versions

[kandersen82]

Matrix build

Description

Run a matrix build to allow running tests on multiple versions of dotnet

Testing

Unable to test before PR is created

[kandersen82]

I just realised that the unit-tests job also packages and uploads artifacts. I am not sure where those artifacts end up or if it will be a problem that the build runs twice.

[blankensteiner]

Closed, as agreed with @kandersen82