minor #449 Fix Swiftmailer deprecation notice (GromNaN)

This PR was merged into the 3.x-dev branch.

Discussion
----------

Fix Swiftmailer deprecation notice

```
Remaining direct deprecation notices (1)

  1x: Since symfony/monolog-bridge 5.4: "Symfony\Bridge\Monolog\Handler\SwiftMailerHandler" is deprecated and will be removed in 6.0.
    1x in XmlMonologExtensionTest::testSingleEmailRecipient from Symfony\Bundle\MonologBundle\Tests\DependencyInjection
```

Commits
-------

43f7232 Fix swiftmailer deprecation notice

Tests/DependencyInjection/FixtureMonologExtensionTest.php

@@ -182,6 +182,7 @@ public function testHandlersWithChannels()
         );
     }
 
+    /** @group legacy */
     public function testSingleEmailRecipient()
     {
         if (\Monolog\Logger::API >= 3) {