Add pg_namespace to ignored regexps

This is to avoid SQL like this:

```sql
SELECT COUNT(*) FROM pg_class c LEFT JOIN pg_namespace n ON n.oid = c.relnamespace WHERE c.relkind in ('v','r') AND c.relname = '<table_name>' AND n.nspname = ANY (current_schemas(false))
```

Could not find any tests for that.

Thanks