* Update third_party-mailman3.de.md
Updating the Postgres DSN to use `postgresql`, as SQLalchemy no longer allows for the use of `postgres`.
* Updating the Postgres DSN to use `postgresql`
Signed-off-by: Aaron Sachs <898627+asachs01@users.noreply.github.com>
---------
Signed-off-by: Aaron Sachs <898627+asachs01@users.noreply.github.com>