Fix a query which triggers an existing bug, see https://github.com/citusdata/citus/issues/3189#issuecomment-571497051

src/test/regress/expected/with_modifying.out

@@ -590,13 +590,17 @@ WITH added_data AS (
 	INSERT INTO modify_table VALUES (1, trunc(10 * random())), (1, trunc(random())) RETURNING *
 ),
 select_data AS (
-	SELECT val, now() FROM added_data WHERE id = 1
+	SELECT val, '2011-01-01' FROM added_data WHERE id = 1
 ),
 raw_data AS (
 	DELETE FROM modify_table WHERE id = 1 AND val IN (SELECT val FROM select_data) RETURNING *
 )
 SELECT COUNT(*) FROM raw_data;
-ERROR:  set-valued function called in context that cannot accept a set
+ count
+---------------------------------------------------------------------
+     2
+(1 row)
+
 INSERT INTO modify_table VALUES (1,2), (1,6), (2, 3), (3, 5);
 WITH select_data AS (
 	SELECT * FROM modify_table

src/test/regress/sql/with_modifying.sql

@@ -358,7 +358,7 @@ WITH added_data AS (
 	INSERT INTO modify_table VALUES (1, trunc(10 * random())), (1, trunc(random())) RETURNING *
 ),
 select_data AS (
-	SELECT val, now() FROM added_data WHERE id = 1
+	SELECT val, '2011-01-01' FROM added_data WHERE id = 1
 ),
 raw_data AS (
 	DELETE FROM modify_table WHERE id = 1 AND val IN (SELECT val FROM select_data) RETURNING *