Uno.UI.RuntimeTests (UnitTestsControl) should run on UWP on the CI

[davidjohnoliver]

What would you like to be added:

Run unit tests in Uno.UI.RuntimeTests on WinUI in the CI build, and fail the build if they don't pass.

Why is this needed:

Two reasons:

• prevent tests that are broken on WinUI (be it in a trivial or non-trivial way) slipping in, which creates friction for other contributors
• PRs with runtime tests included can be merged with more confidence, since the CI vouches for the alignment with UWP

For which Platform:

• [ ] iOS
• [ ] Android
• [ ] WebAssembly
• [ ] WebAssembly renderers for Xamarin.Forms
• [ ] macOS
• [ ] Skia
  • [ ] WPF
  • [ ] GTK (Linux)
  • [ ] Tizen
• [x] Windows
• [ ] Build tasks
• [ ] Solution Templates

Anything else we need to know?

[dr1rrb]

This would also help to:

• Ensure that a newly implemented feature is not accessible only through internal APIs
• Detect behavior changes on WinUI.