Bump NuGet.Packaging from 6.7.0 to 6.8.0

Bumps [NuGet.Packaging](https://github.com/NuGet/NuGet.Client) from 6.7.0 to 6.8.0.
- [Release notes](https://github.com/NuGet/NuGet.Client/releases)
- [Commits](https://github.com/NuGet/NuGet.Client/commits)

---
updated-dependencies:
- dependency-name: NuGet.Packaging
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

src/NuGetizer.Tasks/NuGetizer.Tasks.csproj

@@ -21,7 +21,7 @@
   <ItemGroup>
     <PackageReference Include="Microsoft.SourceLink.GitHub" Version="1.1.1" PrivateAssets="all" />
     <PackageReference Include="Microsoft.Build.Tasks.Core" Version="15.9.20" PrivateAssets="all" />
-    <PackageReference Include="NuGet.Packaging" Version="6.7.0" PrivateAssets="all" />
+    <PackageReference Include="NuGet.Packaging" Version="6.8.0" PrivateAssets="all" />
     <PackageReference Include="NuGet.ProjectManagement" Version="4.2.0" PrivateAssets="all" />
     <PackageReference Include="PolySharp" Version="1.13.2" PrivateAssets="all" />
     <PackageReference Include="ThisAssembly.Project" Version="1.4.1" PrivateAssets="all" />

src/NuGetizer.Tests/NuGetizer.Tests.csproj

@@ -19,7 +19,7 @@
     <PackageReference Include="MSBuild.StructuredLogger" Version="2.2.100" />
     <PackageReference Include="System.IO.Compression" Version="4.3.0" />
     <PackageReference Include="System.IO.Compression.ZipFile" Version="4.3.0" />
-    <PackageReference Include="NuGet.Packaging" Version="6.7.0" />
+    <PackageReference Include="NuGet.Packaging" Version="6.8.0" />
     <PackageReference Include="NuGet.ProjectManagement" Version="4.2.0" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.5.0" />
     <PackageReference Include="Microsoft.TestPlatform.ObjectModel" Version="17.8.0" />