Merge pull request #18018 from yuki24/fix-method-name-inconsistency-in-mailer-example

[guides] Fix method name inconsistency in a mailer example

guides/source/upgrading_ruby_on_rails.md

@@ -231,7 +231,7 @@ class Notifier < ActionMailer::Base
   end
 end
 
-mail = Notifier.notify(user, ...) # Notifier#welcome is not yet called at this point
+mail = Notifier.notify(user, ...) # Notifier#notify is not yet called at this point
 mail = mail.deliver_now           # Prints "Called"
 ```