Fix: rails#52708 Removed credentials from action mailer config documentation.

Author: vikas-tiwari-elitmus

guides/source/action_mailer_basics.md

@@ -893,8 +893,8 @@ config.action_mailer.smtp_settings = {
   address:         'smtp.gmail.com',
   port:            587,
   domain:          'example.com',
-  user_name:       '<username>',
-  password:        '<password>',
+  user_name:       Rails.application.credentials.dig(:smtp, :user_name),
+  password:        Rails.application.credentials.dig(:smtp, :password),
   authentication:  'plain',
   enable_starttls: true,
   open_timeout:    5,