pgagent_upgrade.sql does not exist

Hi PgAdmin Team,

I'm not sure if this is the right channel, but there's mention of pgagent
in the PgAdmin docs [1]. I have been trying to fix a customer's pgagent
install, and this is the following information printed when starting up
pgagent:

```

-bash-4.2$ /usr/edb/as13/bin/pgagent -l2 -f host=127.0.0.1
user=enterprisedb dbname=postgres
Thu Sep 9 20:15:10 2021 DEBUG: Creating primary connection
Thu Sep 9 20:15:10 2021 DEBUG: Parsing connection information...
Thu Sep 9 20:15:10 2021 DEBUG: user: enterprisedb
Thu Sep 9 20:15:10 2021 DEBUG: dbname: postgres
Thu Sep 9 20:15:10 2021 DEBUG: host: 127.0.0.1
Thu Sep 9 20:15:10 2021 DEBUG: Creating DB connection:
user=enterprisedb host=127.0.0.1 dbname=postgres
Thu Sep 9 20:15:10 2021 DEBUG: Database sanity check
Thu Sep 9 20:15:10 2021 ERROR: Unsupported schema version: 3. Version
4 is required - please run pgagent_upgrade.sql.
-bash-4.2$ find /usr/edb/ -name "pgagent_upgrade.sql"
-bash-4.2$

```

Notice that I could not find pgagent_upgrade.sql anywhere. I also looked
in the PgAdmin repository, but could not find it:

```
$ find . -name "pgagent_upgrade.sql"
$ git status
On branch master
Your branch is up to date with 'origin/master'.

nothing to commit, working tree clean
```

I also looked at the pgagent repository (git(at)github(dot)com:postgres/pgagent.git),
and could not find the file. Perhaps this log message is an artifact that
needs to be removed?

FWIW, I managed to fix the customer's pgagent install by executing `ALTER
EXTENSION "pgagent" UPDATE;`, as specified by pg_upgrade.

Please let me know if you need more info here.

Regards,
--Richard

[1]: https://www.pgadmin.org/docs/pgadmin4/development/pgagent.html