Unable to stop pg_cron scheduler

I'm unable to stop pg_cron scheduler, even after I drop the extension. I also tried to restart the cluster and whole postgres service, but the scheduler is still running.

This is an issue, because it maintains connection to the database. In the case I install the extension to database other than postgres, it effectively prevents me from dropping/renaming the database.

It happened both with background workers and libpq connection.

I'd expect that dropping the extension should stop the scheduler.

I'm running postgresql-16-cron 1.6.4-1.pgdg22.04+1

```
postgres=# create extension pg_cron;

postgres=# SELECT pid,datname,application_name FROM pg_stat_activity WHERE datname = 'postgres';
pid | datname | application_name
-------+----------+-------------------
23807 | postgres | pg_cron scheduler
26168 | postgres | psql

postgres=# drop extension pg_cron;

postgres=# SELECT pid,datname,application_name FROM pg_stat_activity WHERE datname = 'postgres';
pid | datname | application_name
-------+----------+-------------------
23807 | postgres | pg_cron scheduler
26168 | postgres | psql
```