BUG #16604: pg_dump with --jobs breaks SSL connections

The following bug has been logged on the website:

Bug reference: 16604
Logged by: Zsolt Ero
Email address: zsolt(dot)ero(at)gmail(dot)com
PostgreSQL version: 12.4
Operating system: Ubuntu 20.04
Description:

I'm using pg_dump in the following syntax:

pg_dump --dbname="sslmode=verify-ca sslrootcert=server-ca.pem \
sslcert=client-cert.pem sslkey=client-key.pem \
hostaddr=1.2.3.4 \
user=postgres dbname=app" \
--format=directory \
--file=dump_app \
--jobs=3

As long as the --jobs parameter is present, the process breaks after
"pg_dump: saving database definition".
It breaks with "FATAL:  connection requires a valid client certificate".

Without --jobs it completes without errors. I also think it's happening with
pg_restore as well.

Client is postgresql-client-12 under Ubuntu 20.04 from latest official
packages (http://apt.postgresql.org/pub/repos/apt).