Build .net 9.0 solution

[DemoBytom]

I'm aware that .net 9.0 is not yet supported by Nuke due to #818, but I managed to get a local build to work as long as both .net 8 and .net 9 SDK are installed, the build project targets a net8.0, and the rest of projects target net9.0 frameworks. But I'm unable to make it work when run on GitHub Actions.

My project is setup as fallows:

global.json //referencing sdk 9.0.100
.sln //referencing projects with <TargetFramework>net9.0</TargetFramework>
/build/global.json //referencing sdk 8.0.100
/build/_build/_builld.csproj //<TargetFramework>net8.0</TargetFramework>
[...]

The build is run on GitHubActionsImage.WindowsLatest. The bootstrapping file detects the root global.json and installs .net 9.0 SDK, but does not detect the nested global.json and does not install the .net 8.0 SDK.

I guess I could fiddle around with the bootsrapping file so that i does detect them both, but I'm unsure if that is the right approach. I've never worked with multi target/multi framework builds, so I have no idea how to best approach it.