build(deps): bump Xamarin.AndroidX.Preference in /samples (#225)

Bumps [Xamarin.AndroidX.Preference](https://github.com/xamarin/AndroidX) from 1.1.1.7 to 1.1.1.8.
- [Release notes](https://github.com/xamarin/AndroidX/releases)
- [Commits](https://github.com/xamarin/AndroidX/commits)

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

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

samples/LoginApp.Android/LoginApp.Android.csproj

@@ -78,7 +78,7 @@
     <PackageReference Include="Xamarin.Google.Android.Material" Version="1.3.0.1" />
     <!-- We are pinning transitive deps versions coming from ReactiveUI.AndroidX.
          See: https://github.com/reactiveui/ReactiveUI.Validation/pull/216#issuecomment-783218308 -->
-    <PackageReference Include="Xamarin.AndroidX.Preference" Version="1.1.1.7" />
+    <PackageReference Include="Xamarin.AndroidX.Preference" Version="1.1.1.8" />
     <PackageReference Include="Xamarin.AndroidX.Fragment" Version="1.3.0.1" />
     <PackageReference Include="Xamarin.AndroidX.RecyclerView" Version="1.1.0.8" />
   </ItemGroup>

samples/LoginApp.Forms.Android/LoginApp.Forms.Android.csproj

@@ -72,7 +72,7 @@
     <PackageReference Include="Xamarin.Android.Support.v7.MediaRouter" Version="28.0.0.3" />
     <PackageReference Include="Xamarin.AndroidX.MediaRouter" Version="1.2.2.1" />
     <PackageReference Include="Xamarin.AndroidX.Palette" Version="1.0.0.7" />
-    <PackageReference Include="Xamarin.AndroidX.Preference" Version="1.1.1.7" />
+    <PackageReference Include="Xamarin.AndroidX.Preference" Version="1.1.1.8" />
   </ItemGroup>
   <ItemGroup>
     <Compile Include="MainActivity.cs" />