Update Complex_Grid_XAML.csproj from .NET Framework net40 to LTS (or current) version

[github-actions]

The Complex_Grid_XAML.csproj project file targets a .NET version which is no longer supported. This is an auto-generated issue, detailed and discussed in dotnet/docs#22271.

See line 10 in dotnet-desktop-guide/samples/snippets/csharp/VS_Snippets_Wpf/GridComplex/CS/Complex_Grid_XAML.csproj.

Target version	End of life	Release notes	Nearest LTS TFM version
v4.0	January, 12 2016	v4.0 release notes	net48

Consider upgrading the project to either the current release, or the nearest LTS TFM version.

If this project is intentionally targeting an unsupported version, you can optionally configure to ignore this automated issue. Create a file at the root of the repository, named dotnet-versionsweeper.json and add an ignore entry following the globbing patterns detailed here.

{
    "ignore": [
        "**/dotnet-desktop-guide/samples/snippets/csharp/VS_Snippets_Wpf/GridComplex/CS/Complex_Grid_XAML.csproj"
    ]
}