Fix cloud test schema mismatch with pyarrow 23.x

Explicitly cast AVG() to DOUBLE in the parameterized query aggregation
test to avoid FlightSQL schema inconsistency between flight info
metadata and actual data batches.

Author: lukekim

tests/test_main.py

@@ -546,7 +546,7 @@ def test_cloud_parameterized_query_aggregation():
     reader = client.query_with_params(
         """SELECT o_orderstatus,
                   COUNT(*) as order_count,
-                  AVG(o_totalprice) as avg_price,
+                  CAST(AVG(o_totalprice) AS DOUBLE) as avg_price,
                   SUM(o_totalprice) as total_price
            FROM tpch.orders
            WHERE o_orderstatus = $1