Invalid CI packaging setup, missing netstandard matrix

[Arlodotexe]

Background

See #250

Problem

Packages that don't support any WinUI major version (2 or 3) won't be built at all by the CI, or will be built erroneously under the existing WinUI 2/3 matrices.

Solution

Create a dedicated CI matrix for building components that don't target WinUI at all.