Disable warnings for non-packable test projects

Author: kzu

src/Directory.Build.props

@@ -43,6 +43,8 @@
 
     <!-- Ensure MSBuild tooling can access package artifacts always via PKG_[PackageId] -->
     <GeneratePathProperty>true</GeneratePathProperty>
+    <!-- Avoid warnings for test projects when we run dotnet pack on the whole solution. -->
+    <WarnOnPackingNonPackableProject>false</WarnOnPackingNonPackableProject>
   </PropertyGroup>
 
   <PropertyGroup Label="Build">