Bump NuGet.Packaging from 6.7.0 to 6.8.0 in /src/code (#1481)

Author: dependabot[bot]

src/code/Microsoft.PowerShell.PSResourceGet.csproj

@@ -17,7 +17,7 @@
     <PackageReference Include="NuGet.Commands" Version="6.7.0" />
     <PackageReference Include="NuGet.Common" Version="6.7.0" />
     <PackageReference Include="NuGet.Configuration" Version="6.7.0" />
-    <PackageReference Include="NuGet.Packaging" Version="6.7.0" />
+    <PackageReference Include="NuGet.Packaging" Version="6.8.0" />
     <PackageReference Include="NuGet.ProjectModel" Version="6.7.0" />
     <PackageReference Include="NuGet.Protocol" Version="6.8.0" />
     <PackageReference Include="PowerShellStandard.Library" Version="7.0.0-preview.1" />