`ALTER EXTENSION UPDATE` and `pg_cron launcher` blocked each other, none of the backends proceed

Hi,

We had an issue where the $title happened.

- It was pg_cron 1.5, and the update was actually a no-op. So, no version upgrade was happening.
- background pg_cron was off
- `pg_cron launcher` was blocked reading `cron.jobs` table, waiting for `AccessShareLock`
- Other backend was running `ALTER EXTENSION pg_cron UPDATE`, which had `AccessExclusiveLock` on `cron.jobs`
- We unfortunately didn't have visibility on what lock `ALTER EXTENSION` was waiting on :( We cancelled the backend doing `alter extension`, and when we tried next time, it finished fine.