bug #19941 [Notifier] Fixes typo (mvhirsch)

This PR was submitted for the 6.1 branch but it was merged into the 6.4 branch instead.

Discussion
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[Notifier] Fixes typo

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I'm targeting 6.1, because this introduced the typo.

Commits
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ec6b103 fixes typo

Author: OskarStark

notifier.rst

@@ -944,7 +944,7 @@ The default behavior for browser channel notifications is to add a
 However, you might prefer to map the importance level of the notification to the
 type of flash message, so you can tweak their style.
 
-you can do that by overriding the default ``notifier.flash_message_importance_mapper``
+You can do that by overriding the default ``notifier.flash_message_importance_mapper``
 service with your own implementation of
 :class:`Symfony\\Component\\Notifier\\FlashMessage\\FlashMessageImportanceMapperInterface`
 where you can provide your own "importance" to "alert level" mapping.