Reenable NuGet publishing to GitHub NuGet registry.

[Konard]

  pushCSharpNuGetToGitHubPackageRegistry:
    needs: testAndDeploy
    if: github.event_name == 'push'
    runs-on: windows-latest
    steps:
      - uses: actions/checkout@v1
        with:
          submodules: true
      - uses: nuget/setup-nuget@v1
      - name: Publish CSharp NuGet to GitHub Package Registry
        run: |
          dotnet build -c Release
          dotnet pack -c Release
          nuget source Add -Name "GitHub" -Source "https://nuget.pkg.github.com/linksplatform/index.json" -UserName linksplatform -Password ${{ secrets.GITHUB_TOKEN }}
          nuget push **/*.nupkg -Source "GitHub" -SkipDuplicate