Deploy nuget without OVFFileConverterGUI

Temporarily removes the `OFVFFileConverterGUI` package from the solution during the nuget deploy. 

Required because even though packing the project is already prevented by the `IsPackable=false` flag in the `.csproj`, dotnet pack still tries to build the project before, which is not possible with `netcore2.1`.

.github/workflows/BuildTestDeploy.yml

@@ -89,6 +89,7 @@ jobs:
                   
     - name: Build Windows
       run: |
+        dotnet sln OpenVectorFormatTools.sln remove OVFFileConverterGUI/OVFFileConverterGUI.csproj
         dotnet build --configuration Release
                   
     - name: Nuget Deploy