Fix auth-source password lookup

* lisp/net/network-stream.el
(network-stream-certificate): Ensure :port is specified as a string to
'auth-source-search' (Bug#38371).

Copyright-paperwork-exempt: yes

lisp/net/network-stream.el

@@ -233,7 +233,7 @@ gnutls-boot (as returned by `gnutls-boot-parameters')."
               (ignore-errors
                 (car (auth-source-search :max 1
                                          :host host
-                                         :port service))))
+                                         :port (format "%s" service)))))
 	     (key (plist-get auth-info :key))
 	     (cert (plist-get auth-info :cert)))
 	(and key cert (file-readable-p key) (file-readable-p cert)