[Messenger] Don't deep merge routing.senders config option

src/Symfony/Bundle/FrameworkBundle/CHANGELOG.md

@@ -16,7 +16,8 @@ CHANGELOG
  * Overriding the methods `KernelTestCase::tearDown()` and `WebTestCase::tearDown()` without the `void` return-type is deprecated.
  * Added new `error_controller` configuration to handle system exceptions
  * Added sort option for `translation:update` command.
- 
+ * [BC Break] The `framework.messenger.routing.senders` config key is not deep merged anymore.
+
 4.3.0
 -----
 

src/Symfony/Bundle/FrameworkBundle/DependencyInjection/Configuration.php

@@ -1162,6 +1162,7 @@ class Configuration implements ConfigurationInterface
                                 })
                             ->end()
                             ->prototype('array')
+                                ->performNoDeepMerging()
                                 ->children()
                                     ->arrayNode('senders')
                                         ->requiresAtLeastOneElement()