fix: allow cast on types with underscores/numbers

e.g. select=oid_array::_int4

test/spec/fixtures/privileges.sql

@@ -179,6 +179,7 @@ GRANT ALL ON TABLE
     , limited_delete_items_cpk_view
     , limited_update_items_cpk_view
     , xmltest
+    , oid_test
 TO postgrest_test_anonymous;
 
 GRANT INSERT ON TABLE insertonly TO postgrest_test_anonymous;