fix(backend): Update MikroORM, Fix voor 'pks not iterable' problem in Groups

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

@@ -35,5 +35,5 @@ export class Assignment {
         entity: () => Group,
         mappedBy: 'assignment',
     })
-    groups!: Collection<Group>;
+    groups: Collection<Group> = new Collection<Group>(this);
 }

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

@@ -7,15 +7,19 @@ import { GroupRepository } from '../../data/assignments/group-repository.js';
     repository: () => GroupRepository,
 })
 export class Group {
-    @ManyToOne({
-        entity: () => Assignment,
-        primary: true,
-    })
-    assignment!: Assignment;
-
+    /*
+     WARNING: Don't move the definition of groupNumber! If it does not come before the definition of assignment,
+     creating groups fails because of a MikroORM bug!
+     */
     @PrimaryKey({ type: 'integer', autoincrement: true })
     groupNumber?: number;
 
+    @ManyToOne({
+        entity: () => Assignment,
+        primary: true
+    })
+    assignment!: Assignment;
+
     @ManyToMany({
         entity: () => Student,
         owner: true,