test_ddl_deparse: rename matview

Should have done this in e69f5e0e ...
Per note from Tom Lane.

src/test/modules/test_ddl_deparse/expected/matviews.out

 --
 -- Materialized views
 --
-CREATE MATERIALIZED VIEW pg_class_mv AS
+CREATE MATERIALIZED VIEW ddl_deparse_mv AS
   SELECT * FROM datatype_table LIMIT 1 WITH NO DATA;
 NOTICE:  DDL test: type simple, tag CREATE MATERIALIZED VIEW
-REFRESH MATERIALIZED VIEW pg_class_mv;
+REFRESH MATERIALIZED VIEW ddl_deparse_mv;
 NOTICE:  DDL test: type simple, tag REFRESH MATERIALIZED VIEW

src/test/modules/test_ddl_deparse/sql/matviews.sql

@@ -2,7 +2,7 @@
 -- Materialized views
 --
 
-CREATE MATERIALIZED VIEW pg_class_mv AS
+CREATE MATERIALIZED VIEW ddl_deparse_mv AS
   SELECT * FROM datatype_table LIMIT 1 WITH NO DATA;
 
-REFRESH MATERIALIZED VIEW pg_class_mv;
+REFRESH MATERIALIZED VIEW ddl_deparse_mv;