fix: remove broken constance cache backend setting for non-Redis environments

The previous commit set CONSTANCE_DATABASE_CACHE_BACKEND = "default" when
no Redis is available, but constance rejects Django's default LocMemCache
because it requires cross-process caching. This silently disabled all
carrier plugins, causing connection creation and validation to fail.

Author: danh91

apps/api/karrio/server/settings/cache.py

@@ -114,6 +114,8 @@
         "Skipping default Redis cache configuration (worker mode - only HUEY Redis needed)"
     )
 else:
-    # No Redis available — cache constance values using Django's default
-    # LocMemCache to avoid N+1 database queries on each config access
-    CONSTANCE_DATABASE_CACHE_BACKEND = "default"
+    # No Redis available — constance will read directly from the database.
+    # We intentionally do NOT set CONSTANCE_DATABASE_CACHE_BACKEND here
+    # because constance rejects Django's default LocMemCache backend
+    # (it requires a cross-process cache like Redis or Memcached).
+    pass

modules/core/karrio/server/providers/tests/test_connections.py

@@ -379,6 +379,7 @@ def test_create_connection(self):
         response = self.client.post(url, SENDLE_CONNECTION_DATA, format="json")
         response_data = json.loads(response.content)
 
+        print(response)
         self.assertEqual(response.status_code, status.HTTP_201_CREATED)
         self.assertDictEqual(response_data, SENDLE_CONNECTION_RESPONSE)