Fix duplicate offense messages in `RuboCop::Cop::Isucon::Mysql2::ManyJoinTable`

[Go Sueyoshi]

rubocop-isucon/spec/rubocop/cop/isucon/mysql2/many_join_table_spec.rb

Lines 13 to 27 in 74c0c14

       expect_offense(<<~RUBY) 
         totals = db.xquery( 
                  ^^^^^^^^^^ Avoid SQL with lots of JOINs 
                  ^^^^^^^^^^ Avoid SQL with lots of JOINs 
           "SELECT IFNULL(SUM(`submissions`.`score`), 0) AS `total_score`" \\ 
           " FROM `users`" \\ 
           " JOIN `registrations` ON `users`.`id` = `registrations`.`user_id`" \\ 
           " JOIN `courses` ON `registrations`.`course_id` = `courses`.`id`" \\ 
           " LEFT JOIN `classes` ON `courses`.`id` = `classes`.`course_id`" \\ 
           " LEFT JOIN `submissions` ON `users`.`id` = `submissions`.`user_id` AND `submissions`.`class_id` = `classes`.`id`" \\ 
           " WHERE `courses`.`id` = ?" \\ 
           " GROUP BY `users`.`id`", 
           course[:id] 
         ).map { |_| _[:total_score] } 
       RUBY