Update System.Collections.Immutable to 8.0.0

Author: Arlodotexe

ProjectHeads/App.Head.Uwp.Dependencies.props

@@ -4,6 +4,6 @@
   <ItemGroup>
     <PackageReference Include="Microsoft.Toolkit.Uwp.UI.Controls.Markdown" Version="7.1.2" />
     <PackageReference Include="Microsoft.Xaml.Behaviors.Uwp.Managed" Version="2.0.1" />
-    <PackageReference Include="System.Collections.Immutable" Version="5.0.0" />
+    <PackageReference Include="System.Collections.Immutable" Version="8.0.0" />
   </ItemGroup>
 </Project>

ToolkitComponent.SampleProject.props

@@ -9,7 +9,7 @@
   <!-- Import this component's source project -->
   <ItemGroup>
     <ProjectReference Include="$(MSBuildProjectDirectory)\..\src\*.csproj" />
-    <PackageReference Condition="'$(IsMacOS)' != 'true'" Include="System.Collections.Immutable" Version="5.0.0" />
+    <PackageReference Condition="'$(IsMacOS)' != 'true'" Include="System.Collections.Immutable" Version="8.0.0" />
   </ItemGroup>
 
   <ItemGroup>