Sending mail via SMTP in Emacs 27.0.50 fails when using the secrets
auth-source backend - this seems to be due to network-stream-certificate
calling auth-source-search with :port specified as an integer - since
then later auth-source-secrets-listify-pattern fails with the following
backtrace as it seems to expect all parameters to be strings.

Attached is a patch to resolve this, in the same way bug#20541 was
solved previously.

I wonder however if it might just be better to make
auth-source-secrets-listify-pattern smarter to handle numeric elements

Debugger entered--Lisp error: (wrong-type-argument sequencep 587)
  mapcar(#f(compiled-function (v) #<bytecode 0x157a1426228d>) 587)
  auth-source-secrets-listify-pattern((:port 587))
  auth-source-secrets-listify-pattern((:host "smtp.server.com" :port 587))
  auth-source-secrets-search(:backend #<auth-source-backend auth-source-backend-157a12d702d8> :type secrets :max 1 :require nil :create nil :delete nil :max 1 :host "smtp.server.com" :port 587)
  apply(auth-source-secrets-search :backend #<auth-source-backend auth-source-backend-157a12d702d8> :type secrets :max 1 :require nil :create nil :delete nil (:max 1 :host "smtp.server.com" :port 587))
  auth-source-search-backends((#<auth-source-backend auth-source-backend-157a12d40ef0> #<auth-source-backend auth-source-backend-157a12d702d8> #<auth-source-backend auth-source-backend-157a12d71808>) (:max 1 :host "smtp.server.com" :port 587) 1 nil nil nil)
  auth-source-search(:max 1 :host "smtp.server.com" :port 587)
  network-stream-certificate("smtp.server.com" 587 (:type nil :return-list t :warn-unless-encrypted nil :capability-command "EHLO slate\15\n" :end-of-command "^[0-9]+ .*\15\n" :success "^2.*\n" :always-query-capabilities t :starttls-function #f(compiled-function (capabilities) #<bytecode 0x157a140f6e29>) :client-certificate t :use-starttls-if-possible t))
  network-stream-open-starttls("smtpmail" #<buffer *trace of SMTP session to smtp.server.com*> "smtp.server.com" 587 (:type nil :return-list t :warn-unless-encrypted nil :capability-command "EHLO slate\15\n" :end-of-command "^[0-9]+ .*\15\n" :success "^2.*\n" :always-query-capabilities t :starttls-function #f(compiled-function (capabilities) #<bytecode 0x157a140f6e29>) :client-certificate t :use-starttls-if-possible t))
  open-network-stream("smtpmail" #<buffer *trace of SMTP session to smtp.server.com*> "smtp.server.com" 587 :type nil :return-list t :warn-unless-encrypted nil :capability-command "EHLO slate\15\n" :end-of-command "^[0-9]+ .*\15\n" :success "^2.*\n" :always-query-capabilities t :starttls-function #f(compiled-function (capabilities) #<bytecode 0x157a140f6e29>) :client-certificate t :use-starttls-if-possible t)
  smtpmail-via-smtp(("foo@bar.com") #<buffer  smtpmail temp>)
  smtpmail-send-it()
  message-use-send-mail-function()
  message--default-send-mail-function()
  message-multi-smtp-send-mail()
  message--send-mail-maybe-partially()
  message-send-mail(nil)
  message-send-via-mail(nil)
  message-send(nil)
  message-send-and-exit(nil)
  funcall-interactively(message-send-and-exit nil)
  call-interactively(message-send-and-exit nil nil)
  command-execute(message-send-and-exit)