Put InternalsVisibleTo in its own group

Terminal.Gui/Terminal.Gui.csproj

@@ -46,6 +46,11 @@
     <PackageReference Include="Wcwidth" Version="2.0.0" />
     <!-- Enable Nuget Source Link for github -->
     <PackageReference Include="Microsoft.SourceLink.GitHub" Version="8.0.0" PrivateAssets="All" />
+  </ItemGroup>
+  <!-- =================================================================== -->
+  <!-- Namespaces for which internal items are visible -->
+  <!-- =================================================================== -->
+  <ItemGroup>
     <InternalsVisibleTo Include="UnitTests" />
   </ItemGroup>
   <PropertyGroup>