fix(backend): Added missing repository-properties to entity annotations

backend/src/entities/users/teacher.entity.ts

@@ -1,8 +1,9 @@
 import { Collection, Entity, ManyToMany } from '@mikro-orm/core';
 import { User } from './user.entity.js';
 import { Class } from '../classes/class.entity.js';
+import {TeacherRepository} from "../../data/users/teacher-repository";
 
-@Entity()
+@Entity({repository: () => TeacherRepository})
 export class Teacher extends User {
     @ManyToMany(() => Class)
     classes!: Collection<Class>;