[ruby/ostruct] Fix class and method as attribute names

ruby/ostruct@7258535073

lib/ostruct.rb

@@ -246,7 +246,7 @@ def new_ostruct_member!(name) # :nodoc:
       if owner.class == ::Class
         owner < ::OpenStruct
       else
-        self.class.ancestors.any? do |mod|
+        self.class!.ancestors.any? do |mod|
           return false if mod == ::OpenStruct
           mod == owner
         end

test/ostruct/test_ostruct.rb

@@ -406,4 +406,10 @@ def test_marshal
     o2 = Marshal.load(Marshal.dump(o))
     assert_equal o, o2
   end
+
+  def test_class
+    os = OpenStruct.new(class: 'my-class', method: 'post')
+    assert_equal('my-class', os.class)
+    assert_equal(OpenStruct, os.class!)
+  end
 end