Merge pull request #17322 from vipulnsward/fix-test-warning

Fixed test throwing unused variable warning

activerecord/test/cases/serialized_attribute_test.rb

@@ -143,7 +143,7 @@ def test_nil_not_serialized_with_class_constraint
   def test_serialized_attribute_should_raise_exception_on_assignment_with_wrong_type
     Topic.serialize(:content, Hash)
     assert_raise(ActiveRecord::SerializationTypeMismatch) do
-      topic = Topic.new(content: 'string')
+      Topic.new(content: 'string')
     end
   end