Move to .NET 8.0

[simon-reynolds]

Hello @TheAngryByrd

I've got a local version of MiniScaffold updated to .NET 8.0, before I submit a drive-by PR I just wanted to check if there was a reason why MiniScaffold still targeted .NET 6.0?

[TheAngryByrd]

Yeah 8 is LTS, let’s do it!

[simon-reynolds]

PR opened as #288