build(deps): update ReactiveUI.Fody requirement in /samples (#446)

Updates the requirements on [ReactiveUI.Fody](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.Fody
  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/LoginApp.csproj

@@ -5,7 +5,7 @@
   </PropertyGroup>
   <ItemGroup>
     <PackageReference Include="ReactiveUI" Version="17.*" />
-    <PackageReference Include="ReactiveUI.Fody" Version="17.*" />
+    <PackageReference Include="ReactiveUI.Fody" Version="18.*" />
     <PackageReference Include="ReactiveUI.Validation" Version="2.*" />
   </ItemGroup>
 </Project>