Android packages not repackable

[Falco20019]

Currently it's not possible to package any newer target frameworks like net6.0-android31.0 since they were not parsable by NuGet.Packaging in version 5.6.0 used by gpr. Support for those was added beginning with 5.8.0.6718. Please update the version of NuGet.Packaging to 5.8.1 or newer.

That's what grp will report.

Uploading package Com.Hoho.Android.UsbSerial 3.4.6 from Com.Hoho.Android.UsbSerial.3.4.6.nupkg ...
Found 1 package.
[Com.Hoho.Android.UsbSerial.3.4.6.nupkg]: Unsupported targetFramework value 'net6.0-android31.0'.
System.IO.InvalidDataException: Unsupported targetFramework value 'net6.0-android31.0'.
   at NuGet.Packaging.ManifestReader.ReadMetadataValue(ManifestMetadata manifestMetadata, XElement element, HashSet`1 allElements)
   at NuGet.Packaging.ManifestReader.ReadMetadata(XElement xElement)
   at NuGet.Packaging.ManifestReader.ReadManifest(XDocument document)
   at NuGet.Packaging.Manifest.ReadFrom(Stream stream, Func`2 propertyProvider, Boolean validateSchema)
   at NuGet.Packaging.PackageBuilder.ReadManifest(Stream stream, String basePath, Func`2 propertyProvider)
   at NuGet.Packaging.PackageBuilder..ctor(Stream stream, String basePath, Func`2 propertyProvider)
   at GprTool.NuGetUtilities.RewriteNupkg(PackageFile packageFile, NuGetVersion nuGetVersion) in /home/runner/work/gpr/gpr/src/GprTool/NuGetUtilities.cs:line 202
   at GprTool.PushCommand.<OnExecuteAsyncImpl>g__UploadPackageAsync|1_3(PackageFile packageFile, NuGetVersion nuGetVersion, String token, IAsyncPolicy`1 retryPolicy, CancellationToken cancellationToken) in /home/runner/work/gpr/gpr/src/GprTool/Program.cs:line 522
   at GprTool.EnumerableExtensions.<>c__DisplayClass0_1`1.<<ForEachAsync>b__1>d.MoveNext() in /home/runner/work/gpr/gpr/src/GprTool/EnumerableExtensions.cs:line 34
--- End of stack trace from previous location ---
   at GprTool.PushCommand.OnExecuteAsyncImpl(CommandLineApplication app, CancellationToken cancellationToken) in /home/runner/work/gpr/gpr/src/GprTool/Program.cs:line 502
   at GprTool.GprCommandBase.OnExecuteAsync(CommandLineApplication app, CancellationToken cancellationToken) in /home/runner/work/gpr/gpr/src/GprTool/Program.cs:line 812
   at McMaster.Extensions.CommandLineUtils.Conventions.ExecuteMethodConvention.InvokeAsync(MethodInfo method, Object instance, Object[] arguments)
   at McMaster.Extensions.CommandLineUtils.Conventions.ExecuteMethodConvention.OnExecute(ConventionContext context, CancellationToken cancellationToken)