Update MultiTarget/PackageReferences/WinAppSdk.props

Resolves https://github.com/CommunityToolkit/Tooling-Windows-Submodule/pull/195/files#r1662838806

Author: Arlodotexe

MultiTarget/PackageReferences/WinAppSdk.props

@@ -4,6 +4,6 @@
     <PackageReference Include="Microsoft.Windows.SDK.BuildTools" Version="10.0.22621.756" />
   </ItemGroup>
   <ItemGroup>
-    <PackageReference Include="Microsoft.Windows.CsWinRT" Version="2.1.0-prerelease.240602.1" />
+    <PackageReference Include="Microsoft.Windows.CsWinRT" Version="2.1.0-prerelease.240602.1" PrivateAssets="all" />
   </ItemGroup>
 </Project>