Add test for anonymous module with private method

This already passes on RuboCop AST 1.0.1 via
rubocop/rubocop-ast@12734b6,
but I think it's worth adding as an integration test anyway, and we can
also now drop the refinement-specific check added in
69700a5.

lib/rubocop/cop/layout/def_end_alignment.rb

@@ -46,7 +46,7 @@ def on_def(node)
         alias on_defs on_def
 
         def on_send(node)
-          return if !node.def_modifier? || node.method?(:using)
+          return unless node.def_modifier?
 
           method_def = node.each_descendant(:def, :defs).first
           expr = node.source_range

spec/rubocop/cop/layout/def_end_alignment_spec.rb

@@ -69,6 +69,17 @@ class << Hash
         RUBY
       end
     end
+
+    context 'when including an anonymous module containing `private def`' do
+      it 'does not register an offense' do
+        expect_no_offenses(<<~RUBY)
+          include Module.new {
+            private def foo
+            end
+          }
+        RUBY
+      end
+    end
   end
 
   context 'when EnforcedStyleAlignWith is def' do