Fix taskdialog vb project (#4068)

Author: adegeo

windowsforms/TaskDialogDemo/vb/TaskDialogDemo.vbproj

@@ -1,8 +1,8 @@
-<Project Sdk="Microsoft.NET.Sdk.WindowsDesktop">
+<Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFramework>net5.0</TargetFramework>
+    <TargetFramework>net5.0-windows</TargetFramework>
     <Nullable>enable</Nullable>
     <UseWindowsForms>true</UseWindowsForms>
   </PropertyGroup>