Add test to ensure tmp:clear works when tmp is missing

See #20299.

railties/test/application/rake_test.rb

@@ -285,5 +285,12 @@ def test_template_load_initializers
 
       assert_match(/Hello, World!/, output)
     end
+
+    def test_tmp_clear_should_work_if_folder_missing
+      FileUtils.remove_dir("#{app_path}/tmp")
+      errormsg = Dir.chdir(app_path) { `bundle exec rake tmp:clear` }
+      assert_predicate $?, :success?
+      assert_empty errormsg
+    end
   end
 end