Fix net46 TFM in VSTestXunitDesktopAndNetCore.csproj

VSTest added validation for the supported TFM in microsoft/vstest#15073 and the package only supports net462

Author: akoeplinger

test/TestAssets/TestProjects/XunitMulti/VSTestXunitDesktopAndNetCore.csproj

@@ -2,10 +2,10 @@
   <Import Project="$([MSBuild]::GetDirectoryNameOfFileAbove($(MSBuildThisFileDirectory), testAsset.props))\testAsset.props" />
 
   <PropertyGroup>
-    <TargetFrameworks>net46;$(CurrentTargetFramework)</TargetFrameworks>
+    <TargetFrameworks>net462;$(CurrentTargetFramework)</TargetFrameworks>
   </PropertyGroup>
 
-  <PropertyGroup Condition="'$(TargetFramework)' == 'net46'">
+  <PropertyGroup Condition="'$(TargetFramework)' == 'net462'">
     <DefineConstants>DESKTOP;$(DefineConstants)</DefineConstants>
   </PropertyGroup>