Patch mail gem to handle TLS settings properly

What does this MR do and why?

While https://github.com/mikel/mail/pull/1526 made it possible to disable STARTTLS with Ruby 3, there were a number of logic errors that were fixed in https://github.com/mikel/mail/pull/1536.

We pull in those changes so that existing users don't have to modify their configurations to omit tls and ssl settings to disable STARTTLS.

Relates to #399241 (closed)

How to set up and validate locally

First, on an Omnibus instance, copy config/initializers/mail_starttls_patch.rb to /opt/gitlab/embedded/service/gitlab-rails/config/initializers.

Verify with STARTTLS enabled

1. Set up Gmail with GitLab: https://kifarunix.com/configure-gitlab-to-use-gmail-smtp-for-outbound-mails/
2. Run gitlab-rails console: Notify.test_email('destination_email@address.com', 'Message Subject', 'Message Body').deliver_now

Verify with STARTTLS disabled

1. Set up Postfix: https://www.digitalocean.com/community/tutorials/how-to-install-and-configure-postfix-as-a-send-only-smtp-server-on-ubuntu-22-04
2. Configure SMTP without SSL: https://docs.gitlab.com/omnibus/settings/smtp.html#smtp-without-ssl
3. Run gitlab-rails console: Notify.test_email('destination_email@address.com', 'Message Subject', 'Message Body').deliver_now

Messages should be sent successfully in both cases.

MR acceptance checklist

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