fix: ProfessorServiceTest assert error

uncomment line to solve the test failure

Author: vianavitor-dev

src/main/java/com/vianavitor/simplelibrarygame/service/ProfessorService.java

@@ -50,7 +50,7 @@ public void register(Professor newProfessor, String classroomCode) throws Duplic
         classroom.getUsers().add(professor);
 
         classroomRepository.save(classroom);
-//        newProfessor.getClassrooms().add(classroom);
+        newProfessor.getClassrooms().add(classroom);
     }
 
     public List<Professor> getAll() {