Update maintenance-postgres.md

Seems that borg backup support was added by the commit b61b908

docs/maintenance-postgres.md

@@ -87,8 +87,6 @@ This playbook can upgrade your existing Postgres setup with the following comman
 just run-tags upgrade-postgres
 ```
 
-**Warning: If you're using Borg Backup keep in mind that there is no official Postgres 16 support yet.**
-
 **The old Postgres data directory is backed up** automatically, by renaming it to `/matrix/postgres/data-auto-upgrade-backup`.
 To rename to a different path, pass some extra flags to the command above, like this: `--extra-vars="postgres_auto_upgrade_backup_data_path=/another/disk/matrix-postgres-before-upgrade"`