Fix first PHPStan error

Author: vmcj

webapp/src/Service/DOMJudgeService.php

@@ -24,6 +24,7 @@
 use App\Entity\ProblemAttachment;
 use App\Entity\QueueTask;
 use App\Entity\Rejudging;
+use App\Entity\ScoreCache;
 use App\Entity\Submission;
 use App\Entity\Team;
 use App\Entity\TeamAffiliation;