build(deps): update ReactiveUI.WinForms requirement in /samples (#448)

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...18.0.10)

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

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

samples/LoginApp.WinForms/LoginApp.WinForms.csproj

@@ -6,7 +6,7 @@
     </PropertyGroup>
 
     <ItemGroup>
-        <PackageReference Include="ReactiveUI.WinForms" Version="17.*" />
+        <PackageReference Include="ReactiveUI.WinForms" Version="18.*" />
     </ItemGroup>
 
     <ItemGroup>