Fix crash while trying grade an opponent

Caused by missing @Transactional

core/src/main/java/se/su/dsv/scipro/report/GradingReportServiceImpl.java

@@ -48,6 +48,7 @@ public class GradingReportServiceImpl implements GradingReportTemplateService, G
     }
 
     @Override
+    @Transactional
     public boolean updateOppositionCriteria(SupervisorGradingReport report, FinalSeminarOpposition opposition) {
         for (GradingCriterion gradingCriterion : report.getIndividualCriteria()) {
             boolean isOppositionCriterion = gradingCriterion.getFlag() == GradingCriterion.Flag.OPPOSITION;