Fix unit test

Author: WaVEV

django_mongodb_backend/lookups.py

@@ -59,17 +59,17 @@ def get_subquery_wrapping_pipeline(self, compiler, connection, field_name, expr)
             "$group": {
                 "_id": None,
                 # use a temporal name in order to support field_name="_id"
-                "tmp_name": {"$addToSet": expr.as_mql(compiler, connection, as_expr=True)},
+                "subquery_results": {"$addToSet": expr.as_mql(compiler, connection, as_expr=True)},
             }
         },
         # Workaround for https://jira.mongodb.org/browse/SERVER-114196:
         # $$NOW becomes unavailable after $unionWith, so it must be stored
         # beforehand to ensure it remains accessible later in the pipeline.
         {"$addFields": {"__now": "$$NOW"}},
         # Add an empty extra document to handle default values on empty results.
-        {"$unionWith": {"pipeline": [{"$documents": [{"tmp_name": []}]}]}},
+        {"$unionWith": {"pipeline": [{"$documents": [{"subquery_results": []}]}]}},
         {"$limit": 1},
-        {"$project": {field_name: "$tmp_name"}},
+        {"$project": {field_name: "$subquery_results"}},
     ]