Add sshd-session to openssh-server-udeb.install

Starting from OpenSSH 9.8, the ssh server is split into two parts: sshd and sshd-session. See: https://lore.kernel.org/buildroot/0731d879-631d-49af-9c42-57ae774471ba@mind.be/T/

sshd-session seems to be missing in the udeb. As such, setting up the ssh console in the installer always fails.

This MR attempts to fix that.