Adjust regression tests for error message change

src/test/regress/expected/prepared_xacts.out

@@ -134,7 +134,7 @@ SELECT * FROM pxtest1;
 -- This should fail, because the two transactions have a write-skew anomaly
 INSERT INTO pxtest1 VALUES ('fff');
 ERROR:  could not serialize access due to read/write dependencies among transactions
-DETAIL:  Canceled on identification as a pivot, during write.
+DETAIL:  Reason code: Canceled on identification as a pivot, during write.
 HINT:  The transaction might succeed if retried.
 PREPARE TRANSACTION 'foo5';
 SELECT gid FROM pg_prepared_xacts;