Actually accept non-symbols as IDs in erc-open

Actually accept non-symbols as IDs in erc-open

* lisp/erc/erc.el (erc-generate-new-buffer-name): Despite what it says
in the documentation, only symbols were being accepted as valid `:id'
entry-point arguments.  This uses the interned `princ' representation
of the argument instead.
* test/lisp/erc/erc-scenarios-base-netid-samenet.el
(erc-scenarios-common--base-network-id-same-network): Randomly specify
a string for the ID param instead of a non-nil symbol when opening a
new connection.
* test/lisp/erc/resources/erc-scenarios-common.el
(erc-scenarios-common-assert-initial-buf-name): Adjust helper to allow
for non-symbol IDs.  (Bug#59976.)