csharp change language version to 9.0

                
                        <Project Sdk="Microsoft.NET.Sdk">	
  <PropertyGroup>
    <OutputType>Exe</OutputType>
	<LangVersion>9.0</LangVersion>
    <TargetFramework>netcoreapp3.1</TargetFramework>
  </PropertyGroup>

  <ItemGroup>
  </ItemGroup>

</Project>