build: Add package dependencies for .NET 5+

Author: twpol

Source/ORTS.Content/ORTS.Content.csproj

@@ -18,5 +18,6 @@
     <PackageReference Include="Microsoft.DotNet.UpgradeAssistant.Extensions.Default.Analyzers" Version="0.4.355802">
       <PrivateAssets>all</PrivateAssets>
     </PackageReference>
+    <PackageReference Include="Microsoft.Win32.Registry" Version="5.0.0" />
   </ItemGroup>
 </Project>