Use Django 4.1 (soon 4.2) to use the new async framework

Signed-off-by: Emmy D'Anello <emmy.danello@animath.fr>

registration/migrations/0006_alter_registration_polymorphic_ctype.py

@@ -0,0 +1,25 @@
+# Generated by Django 4.1.7 on 2023-03-22 11:22
+
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ("contenttypes", "0002_remove_content_type_name"),
+        ("registration", "0005_studentregistration_vaccine_sheet"),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name="registration",
+            name="polymorphic_ctype",
+            field=models.ForeignKey(
+                editable=False,
+                null=True,
+                on_delete=django.db.models.deletion.CASCADE,
+                related_name="polymorphic_%(app_label)s.%(class)s_set+",
+                to="contenttypes.contenttype",
+            ),
+        ),
+    ]