Support both net7 and net8 at once

[van800]

I had only net8 installed, so I had to make some changes to allow both net7 and net8

[MikeSchulze]

Thank you made it

[MikeSchulze]

hm, with .Net8 the test adapter breaks in VSCode
I'll have to take a look at why this no longer works with .NET8

[van800]

This actually doesn't block me now, you may just revert the whole pull request, if you feel like. I wanted to help, not to create additional work for you.

[MikeSchulze]

I found the issue, the projects using Godot do not separate the build output for .NET7 and .NET8, it saves just to .godot
I set the default for this project to .NET8 now and it works

But with .NET8 a lot of new warnings pops up and needs to be fixed as well.
I'm actual working on it, but thanks for your preparing ;)

Continue here -> #63

[MikeSchulze]

Perhaps you have an idea where these warnings come from

CSC : warning AD0001: Analyzer 'Godot.SourceGenerators.MustBeVariantAnalyzer' threw an exception of type 'System.NullReferenceException' with message 'Object reference not set to an instance of an object.'. [/home/runner/work/gdUnit4Mono/gdUnit4Mono/test/gdUnit4Test.csproj::TargetFramework=net8.0]

[van800]

It is from the Godot sources, however I don't know much
https://github.com/godotengine/godot/issues?q=AD0001%3A+