🔇(backend) fix E010 Django warning logs

Room model uses a default value for its configuration.
However, I used a wrong default value, it should be a callable.

Align the code with Magnify.

src/backend/core/migrations/0003_alter_room_configuration.py

@@ -0,0 +1,18 @@
+# Generated by Django 5.0.7 on 2024-08-07 14:38
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('core', '0002_create_pg_trgm_extension'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='room',
+            name='configuration',
+            field=models.JSONField(blank=True, default=dict, help_text='Values for Visio parameters to configure the room.', verbose_name='Visio room configuration'),
+        )
+    ]

src/backend/core/models.py

@@ -296,7 +296,7 @@ class Room(Resource):
 
     configuration = models.JSONField(
         blank=True,
-        default={},
+        default=dict,
         verbose_name=_("Visio room configuration"),
         help_text=_("Values for Visio parameters to configure the room."),
     )