manager: make agenda's groups foldable (#85616)

tests/manager/test_category.py

@@ -104,7 +104,7 @@ def test_category_fold_preferences(app, admin_user):
     category1 = Category.objects.create(label='Foo bar')
     category2 = Category.objects.create(label='Toto')
 
-    agenda1 = Agenda.objects.create(label='Foo bar', category=category1)
+    Agenda.objects.create(label='Foo bar', category=category1)
     agenda2 = Agenda.objects.create(label='Titi', category=category2)
 
     app = login(app)
@@ -137,7 +137,7 @@ def test_category_fold_preferences(app, admin_user):
 
     # Order is preserved when adding a new category : preferences are preserved
     category3 = Category.objects.create(label='Tata')
-    agenda3 = Agenda.objects.create(label='Titi', category=category3)
+    Agenda.objects.create(label='Titi', category=category3)
 
     user_prefs.update_preference('folded-admin-forms-group-1', False)
     user_prefs.update_preference('folded-admin-forms-group-2', True)