bug #40246 [EventDispatcher] fix registering subscribers twice on edg…

…e-case (nicolas-grekas)

This PR was merged into the 5.2 branch.

Discussion
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[EventDispatcher] fix registering subscribers twice on edge-case

| Q             | A
| ------------- | ---
| Branch?       | 5.2
| Bug fix?      | yes
| New feature?  | no
| Deprecations? | no
| Tickets       | -
| License       | MIT
| Doc PR        | -

Introduced on 5.1 in #36243

Commits
-------

ad60072 [EventDispatcher] fix registering subscribers twice on edge-case

src/Symfony/Component/EventDispatcher/DependencyInjection/RegisterListenersPass.php

@@ -149,7 +149,7 @@ public function process(ContainerBuilder $container)
                     continue;
                 }
 
-                $dispatcherDefinitions[] = $container->getDefinition($attributes['dispatcher']);
+                $dispatcherDefinitions[$attributes['dispatcher']] = $container->getDefinition($attributes['dispatcher']);
             }
 
             if (!$dispatcherDefinitions) {