bug symfony#15409 [Notifier] [Slack] Fixing use example (eesnaola)

This PR was merged into the 5.3 branch.

Discussion
----------

[Notifier] [Slack] Fixing use example

The right class is `SlackImageBlockElement`

Commits
-------

a0df26b Update chatters.rst

Author: OskarStark

notifier/chatters.rst

@@ -59,7 +59,7 @@ to add some interactive options called `Block elements`_::
 
     use Symfony\Component\Notifier\Bridge\Slack\Block\SlackActionsBlock;
     use Symfony\Component\Notifier\Bridge\Slack\Block\SlackDividerBlock;
-    use Symfony\Component\Notifier\Bridge\Slack\Block\SlackImageBlock;
+    use Symfony\Component\Notifier\Bridge\Slack\Block\SlackImageBlockElement;
     use Symfony\Component\Notifier\Bridge\Slack\Block\SlackSectionBlock;
     use Symfony\Component\Notifier\Bridge\Slack\SlackOptions;
     use Symfony\Component\Notifier\Message\ChatMessage;