use NETCoreSdkVersion instead of SdkAnalysisLevel

Author: SimonCropp

src/Directory.Build.props

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="utf-8"?>
 <Project>
   <PropertyGroup>
-    <Version>6.6.2</Version>
+    <Version>6.6.3</Version>
     <AssemblyVersion>1.0.0</AssemblyVersion>
     <PackageTags>Polyfill</PackageTags>
     <DisableImplicitNamespaceImports>true</DisableImplicitNamespaceImports>

src/Polyfill/Polyfill.targets

@@ -4,7 +4,7 @@
     <LowerFramework>$(TargetFramework.ToLower())</LowerFramework>
     <LowerFrameworks>$(TargetFrameworks.ToLower())</LowerFrameworks>
   </PropertyGroup>
-  <PropertyGroup Condition="$([MSBuild]::VersionGreaterThanOrEquals($(SdkAnalysisLevel), '9'))">
+  <PropertyGroup Condition="'$(NETCoreSdkVersion)' != '' AND $([MSBuild]::VersionGreaterThanOrEquals($(NETCoreSdkVersion), '9'))">
     <DefineConstants Condition="$(LangVersion) == '13'">$(DefineConstants);LangVersion13</DefineConstants>
     <DefineConstants Condition="$(LangVersion) == 'latest'">$(DefineConstants);LangVersion13</DefineConstants>
     <DefineConstants Condition="$(LangVersion) == 'preview'">$(DefineConstants);LangVersion13</DefineConstants>