Replace magic priority values with constants

Otherwise there is a hidden dependency between the 'actual' constants, and these constants.
So instead of `-9` use `JudgeTask::PRIORITY_HIGH + 1` and instead of `9` use `JudgeTask::PRIORITY_LOW - 1`.

Suggested-by: Mart Pluijmaekers <[email protected]>

Author: Kevinjil

webapp/src/Service/ExternalContestSourceService.php

@@ -1905,9 +1905,9 @@ protected function getAnalystRunPriority(ExternalRun $run): int | null {
             // We often do not get new useful information for judging correct testcases.
             'correct' => null,
             // Wrong answers are interesting for the analysts, assign a high priority but below manual judging.
-            'wrong-answer' => -9,
+            'wrong-answer' => JudgeTask::PRIORITY_HIGH + 1,
             // Compile errors could be interesting to see what went wrong, assign a low priority.
-            'compiler-error' => 9,
+            'compiler-error' => JudgeTask::PRIORITY_LOW - 1,
             // Otherwise, judge with normal priority.
             default => 0,
         };