Correct error message for row-level triggers with transition tables on partitioned tables.

"Triggers on partitioned tables cannot have transition tables." is
incorrect as we allow statement-level triggers on partitioned tables to
have transition tables.

This has been wrong since commit 86f57594; back-patch to v11 where that
commit came in.

Reviewed by Tom Lane.

Discussion: https://postgr.es/m/CAPmGK17gk4vXLzz2iG%2BG4LWRWCoVyam70nZ3OuGm1hMJwDrhcg%40mail.gmail.com

src/backend/commands/trigger.c

@@ -249,7 +249,7 @@ CreateTriggerFiringOn(CreateTrigStmt *stmt, const char *queryString,
 						(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 						 errmsg("\"%s\" is a partitioned table",
 								RelationGetRelationName(rel)),
-						 errdetail("Triggers on partitioned tables cannot have transition tables.")));
+						 errdetail("ROW triggers with transition tables are not supported on partitioned tables.")));
 		}
 	}
 	else if (rel->rd_rel->relkind == RELKIND_VIEW)

src/test/regress/expected/triggers.out

@@ -2020,7 +2020,7 @@ create trigger failed after update on parted_trig
   referencing old table as old_table
   for each row execute procedure trigger_nothing();
 ERROR:  "parted_trig" is a partitioned table
-DETAIL:  Triggers on partitioned tables cannot have transition tables.
+DETAIL:  ROW triggers with transition tables are not supported on partitioned tables.
 drop table parted_trig;
 --
 -- Verify trigger creation for partitioned tables, and drop behavior