build(deps): update ReactiveUI.WPF requirement in /samples (#444)

Updates the requirements on [ReactiveUI.WPF](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.WPF
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

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

samples/LoginApp.Wpf/LoginApp.Wpf.csproj

@@ -8,7 +8,7 @@
 
   <ItemGroup>
     <PackageReference Include="MahApps.Metro" Version="2.4.9" />
-    <PackageReference Include="ReactiveUI.WPF" Version="17.*" />
+    <PackageReference Include="ReactiveUI.WPF" Version="18.*" />
   </ItemGroup>
 
   <ItemGroup>