only check TFMs when GeneratePackageOnBuild is true (#197)

Author: SimonCropp

src/Directory.Build.props

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="utf-8"?>
 <Project>
   <PropertyGroup>
-    <Version>6.1.0</Version>
+    <Version>6.1.1</Version>
     <AssemblyVersion>1.0.0</AssemblyVersion>
     <PackageTags>Polyfill</PackageTags>
     <DisableImplicitNamespaceImports>true</DisableImplicitNamespaceImports>

src/Polyfill/Polyfill.targets

@@ -61,7 +61,7 @@
   <Target
       Name="PolyfillValidateNugetTargets"
       AfterTargets="AfterBuild"
-      Condition="$(NoWarn.Contains('PolyfillTargetsForNuget')) != true">
+      Condition="$(NoWarn.Contains('PolyfillTargetsForNuget')) != true And '$(GeneratePackageOnBuild)' == 'true'">
     <Warning
         Code="PolyfillTargetsForNuget"
         Text="Projects that produce a nuget and consume Polyfill: