Use default argument in test

We should use a default argument so that when there is only one option
we can delete the arguments instead of updating all the callers.

railties/test/application/rake/multi_dbs_test.rb

@@ -85,7 +85,7 @@ def db_migrate_and_schema_cache_dump_and_schema_cache_clear
         end
       end
 
-      def db_migrate_and_schema_dump_and_load(schema_format)
+      def db_migrate_and_schema_dump_and_load(schema_format = "ruby")
         add_to_config "config.active_record.schema_format = :#{schema_format}"
         require "#{app_path}/config/environment"
 
@@ -428,7 +428,7 @@ def generate_models_for_animals
       end
 
       test "db:migrate and db:schema:dump and db:schema:load works on all databases" do
-        db_migrate_and_schema_dump_and_load "ruby"
+        db_migrate_and_schema_dump_and_load
       end
 
       test "db:migrate and db:schema:dump and db:schema:load works on all databases with sql option" do
@@ -692,7 +692,7 @@ class TwoMigration < ActiveRecord::Migration::Current
         ENV.delete "RAILS_ENV"
         ENV.delete "RACK_ENV"
 
-        db_migrate_and_schema_dump_and_load "ruby"
+        db_migrate_and_schema_dump_and_load
 
         app_file "db/seeds.rb", <<-RUBY
           print Book.connection.pool.db_config.database