No tests for IL2028

A quick control+f search found no tests for [IL2028](https://github.com/dotnet/linker/blob/main/docs/error-codes.md#il2028-attribute-attribute-doesnt-have-the-required-number-of-parameters-specified). This warning shouldn't occur often, though. As far as I can tell it requires defining your own `System.Diagnostics.CodeAnalysis` namespace that includes a new definition for a linker attribute and compiling with `/nostdlib`, so this should be low priority.