use public Module#include instead of send :include

Follow up to #18767

actionpack/test/controller/integration_test.rb

@@ -145,7 +145,7 @@ class IntegrationTestTest < ActiveSupport::TestCase
         name.to_s == "foo" ? "pass" : super
       end
     end
-    @test.class.superclass.__send__(:include, mixin)
+    @test.class.superclass.include(mixin)
     begin
       assert_equal "pass", @test.foo
     ensure

activerecord/test/cases/test_fixtures_test.rb

@@ -3,7 +3,7 @@ require "cases/helper"
 class TestFixturesTest < ActiveRecord::TestCase
   setup do
     @klass = Class.new
-    @klass.send(:include, ActiveRecord::TestFixtures)
+    @klass.include(ActiveRecord::TestFixtures)
   end
 
   def test_deprecated_use_transactional_fixtures=

activesupport/test/concern_test.rb

@@ -76,7 +76,7 @@ class ConcernTest < ActiveSupport::TestCase
   end
 
   def test_class_methods_are_extended_only_on_expected_objects
-    ::Object.__send__(:include, Qux)
+    ::Object.include(Qux)
     Object.extend(Qux::ClassMethods)
     # module needs to be created after Qux is included in Object or bug won't
     # be triggered