fix: import errors van gabe gefixt, teacher en student abstractie weggedaan

backend/src/entities/assignments/assignment.entity.ts

@@ -51,5 +51,5 @@ export class Assignment {
         },
         mappedBy: 'assignment',
     })
-    groups!: Collection<Group>;
+    groups!: Group[];
 }

backend/src/entities/assignments/group.entity.ts

@@ -1,6 +1,7 @@
 import { Collection, Entity, ManyToMany, ManyToOne, PrimaryKey } from '@mikro-orm/core';
 import { Assignment } from './assignment.entity.js';
 import { Student } from '../users/student.entity.js';
+import { GroupRepository } from '../../data/assignments/group-repository.js';
 
 @Entity({
     repository: () => {