[Mailer][MailchimpBridge] Fix incorrect sender address when sender has name

This fixes the same problem as symfony/symfony@6dbac13 but for HTTP transport.

Author: vilius-g

Mailchimp/Http/MandrillTransport.php

@@ -42,7 +42,7 @@ protected function doSend(SentMessage $message): void
             'json' => [
                 'key' => $this->key,
                 'to' => $this->stringifyAddresses($envelope->getRecipients()),
-                'from_email' => $envelope->getSender()->toString(),
+                'from_email' => $envelope->getSender()->getAddress(),
                 'raw_message' => $message->toString(),
             ],
         ]);