minor symfony#12033 [Messenger] Fix hidden section title (ogizanagi)

This PR was merged into the 4.2 branch.

Discussion
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[Messenger] Fix hidden section title

Problem is this section title is hidden on https://symfony.com/doc/current/messenger/handler_results.html (as every other `.section h1`)

Commits
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86ce39f [Messenger] Fix hidden section title

Author: javiereguiluz

messenger/handler_results.rst

@@ -26,7 +26,7 @@ The :method:`Symfony\\Component\\Messenger\\HandleTrait::handle` method ensures
 there is exactly one handler registered and returns its result.
 
 Working with Command & Query Buses
-----------------------------------
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 The Messenger component can be used in CQRS architectures where command & query
 buses are central pieces of the application. Read Martin Fowler's