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>
 
  <PropertyGroupLabel="Build">