Allow querying auth-source with port as string in ERC

Allow querying auth-source with port as string in ERC

* lisp/erc/erc.el (erc--auth-source-determine-params-defaults): Allow
arbitrary strings for `ers-session-port'.  Previously, if a port/service
was any string other than "irc", the auth-source query would fail for a
seemingly unknown reason.  Restricting the value to "irc" is unnecessary
since "irc" is already added to the list of ports, and
`make-network-process' already consults /etc/services for well-known
service names, like "ircs-u", etc.  This change allows a user to (setopt
erc-port "1234"), intentionally or accidentally, while still being able
to use .authinfo for password management.  (Bug#74516)

Copyright-paperwork-exempt: yes
(cherry picked from commit d899519221b23a895672a100f63410ffb8b8b1e4)