minor #13429 Update multiple_buses.rst (Braxilior)

This PR was submitted for the 5.0 branch but it was merged into the 4.4 branch instead (closes #13429).

Discussion
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Update multiple_buses.rst

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Commits
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d37e7d7 Update multiple_buses.rst

Author: javiereguiluz

messenger/multiple_buses.rst

@@ -188,11 +188,11 @@ the correct tag:
                 <!-- command handlers -->
                 <prototype namespace="App\MessageHandler\" resource="%kernel.project_dir%/src/MessageHandler/*CommandHandler.php" autoconfigure="false">
                     <tag name="messenger.message_handler" bus="command.bus"/>
-                </service>
+                </prototype>
                 <!-- query handlers -->
                 <prototype namespace="App\MessageHandler\" resource="%kernel.project_dir%/src/MessageHandler/*QueryHandler.php" autoconfigure="false">
                     <tag name="messenger.message_handler" bus="query.bus"/>
-                </service>
+                </prototype>
             </services>
         </container>