Fix regression in inclusion of analyzer's built-in AdditionalFiles

Author: AArnott

src/Microsoft.VisualStudio.Threading.JointPackage/Microsoft.VisualStudio.Threading.JointPackage.csproj

@@ -13,8 +13,8 @@
   </ItemGroup>
 
   <ItemGroup>
-    <ProjectReference Include="..\Microsoft.VisualStudio.Threading.Analyzers.CodeFixes\Microsoft.VisualStudio.Threading.Analyzers.CodeFixes.csproj" />
-    <ProjectReference Include="..\Microsoft.VisualStudio.Threading\Microsoft.VisualStudio.Threading.csproj" />
+    <ProjectReference Include="..\Microsoft.VisualStudio.Threading.Analyzers.CodeFixes\Microsoft.VisualStudio.Threading.Analyzers.CodeFixes.csproj" PrivateAssets="none" />
+    <ProjectReference Include="..\Microsoft.VisualStudio.Threading\Microsoft.VisualStudio.Threading.csproj" PrivateAssets="none" />
   </ItemGroup>
 
 </Project>