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

[sue445]

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