Handle alias_cols=False cases when resolving columns.

Author: WaVEV

django_mongodb/expressions.py

@@ -53,7 +53,9 @@ def case(self, compiler, connection):
 def col(self, compiler, connection):  # noqa: ARG001
     # If the column is part of a subquery and belongs to one of the parent
     # queries, it will be stored for reference using $let in a $lookup stage.
-    if (
+    # If the query is built with `alias_cols=False`, the column is treated
+    # as belonging to the current collection.
+    if self.alias is not None and (
         self.alias not in compiler.query.alias_refcount
         or compiler.query.alias_refcount[self.alias] == 0
     ):