Rewrite warning related tests

These tests are based on PL-PGSQL usage, triggering warnings. They do not working with the CRDB compatible PL-PGSQL. We need to rewrite them.

- [ ] test_ignores_warnings_when_behaviour_ignore
- [ ] test_logs_warnings_when_behaviour_log
- [ ] test_raises_warnings_when_behaviour_raise
- [ ] test_reports_when_behaviour_report
- [ ] test_warnings_behaviour_can_be_customized_with_a_proc
- [ ] test_allowlist_of_warnings_to_ignore
- [ ] test_allowlist_of_warning_codes_to_ignore

This is the failing PL-PGSQL:

```sql
do $$ BEGIN RAISE WARNING 'PostgreSQL SQL warning'; END; $$
```