build(deps): bump ReactiveUI.Uwp from 18.2.5 to 18.3.1 in /samples (#479

)

Bumps [ReactiveUI.Uwp](https://github.com/reactiveui/reactiveui) from 18.2.5 to 18.3.1.
- [Release notes](https://github.com/reactiveui/reactiveui/releases)
- [Commits](reactiveui/ReactiveUI@18.2.5...18.3.1)

---
updated-dependencies:
- dependency-name: ReactiveUI.Uwp
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

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

samples/LoginApp.Uwp/LoginApp.Uwp.csproj

@@ -151,7 +151,7 @@
     <PackageReference Include="Microsoft.NETCore.UniversalWindowsPlatform" Version="6.2.14" />
     <PackageReference Include="ReactiveUI" Version="18.*" />
     <PackageReference Include="ReactiveUI.Uwp">
-      <Version>18.2.5</Version>
+      <Version>18.3.1</Version>
     </PackageReference>
     <PackageReference Include="ReactiveUI.Validation" Version="3.*" />
   </ItemGroup>