default spark session timezone to UTC in test (#494)

Author: kevinjqliu

tests/conftest.py

@@ -1961,6 +1961,7 @@ def spark() -> SparkSession:
 
     spark = (
         SparkSession.builder.appName("PyIceberg integration test")
+        .config("spark.sql.session.timeZone", "UTC")
         .config("spark.sql.extensions", "org.apache.iceberg.spark.extensions.IcebergSparkSessionExtensions")
         .config("spark.sql.catalog.integration", "org.apache.iceberg.spark.SparkCatalog")
         .config("spark.sql.catalog.integration.catalog-impl", "org.apache.iceberg.rest.RESTCatalog")