From T270732: Upgrade doctrine/dbal from 2.10.4 to 3.0.x for PHP 8.0 support, bumping doctrine to 3.0.0 for PHP 8.0 support, we lose PG 9.2 and 9.3 support...
https://www.postgresql.org/support/versioning/ - 9.4 was first released December 18, 2014, and final release is February 13, 2020. So it's already EOL
Debian oldstable is on 9.6, so I don't think this is a major issue
Basically, this tasks for updating of version checking in MW core, Documentation etc