build(deps): update ReactiveUI.WinForms requirement in /samples (#471)

Updates the requirements on [ReactiveUI.WinForms](https://github.com/reactiveui/reactiveui) to permit the latest version.
- [Release notes](https://github.com/reactiveui/reactiveui/releases)
- [Commits](reactiveui/ReactiveUI@17.0.1...18.2.5)

---
updated-dependencies:
- dependency-name: ReactiveUI.WinForms
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>