bug #31458 [TwigBundle] Fix Mailer integration in Twig (fabpot)

This PR was merged into the 4.3 branch.

Discussion
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[TwigBundle] Fix Mailer integration in Twig

| Q             | A
| ------------- | ---
| Branch?       | 4.3
| Bug fix?      | yes
| New feature?  | no <!-- please update src/**/CHANGELOG.md files -->
| BC breaks?    | no     <!-- see https://symfony.com/bc -->
| Deprecations? | no <!-- please update UPGRADE-*.md and src/**/CHANGELOG.md files -->
| Tests pass?   | yes    <!-- please add some, will be required by reviewers -->
| Fixed tickets | #31449
| License       | MIT
| Doc PR        | n/a

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Commits
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53b68afec4 [TwigBundle] fixed Mailer integration in Twig

src/Symfony/Bundle/TwigBundle/Resources/config/mailer.xml

@@ -6,8 +6,9 @@
 
     <services>
         <service id="twig.mailer.message_listener" class="Symfony\Component\Mailer\EventListener\MessageListener">
-            <argument />
+            <argument>null</argument>
             <argument type="service" id="twig.mime_body_renderer" />
+            <tag name="kernel.event_subscriber"/>
         </service>
 
         <service id="twig.mime_body_renderer" class="Symfony\Bridge\Twig\Mime\BodyRenderer">