backup: ttrss: password authentication failed for user "ttrss"

After restoring a backup I get this error message when trying to open tt-rss:

Exception while creating PDO object:SQLSTATE[08006] [7] FATAL:  password authentication failed for user "ttrss"
FATAL:  password authentication failed for user "ttrss"

I could reproduce the issue from a Rasperry Pi 4, a Pioneer and Vagrant.

It's also come up in the forum more than once:

https://discuss.freedombox.org/t/error-restoring-backup-tt-rss/871

https://discuss.freedombox.org/t/error-restoring-tt-rss-from-backup/376

https://discuss.freedombox.org/t/tiny-tiny-rss-failed-to-install/161

And was fixed in: #1303 (closed)