bug#9298: 23.3.50; Warning: defvar ignored because auth-source-creation-prompts is let-bound

[Leo]

In smtpmail-try-auth-methods from smtpmail.el,
auth-source-creation-prompts is let-bound while `auth-source-search'
triggers loading auth-source.el. This results in void variable
auth-source-creation-prompts.

Looks like autoload is not suitable for use in this case. Maybe just
(require 'auth-source) in the beginning of smtpmail-try-auth-methods.

Debugger entered--Lisp error: (void-variable auth-source-creation-prompts)
  eval(auth-source-creation-prompts)
  ad-Orig-eval-expression(auth-source-creation-prompts nil)
  (setq ad-return-value (ad-Orig-eval-expression eval-expression-arg 
eval-expression-insert-value))
  (let (ad-return-value) (setq ad-return-value (ad-Orig-eval-expression 
eval-expression-arg eval-expression-insert-value)) ad-return-value)
  eval-expression(auth-source-creation-prompts nil)
  call-interactively(eval-expression nil nil)

Leo