minor symfony#27052 [FrameworkBundle] Add Messenger tags to unused whitelist (chalasr)

This PR was merged into the 4.1-dev branch.

Discussion
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[FrameworkBundle] Add Messenger tags to unused whitelist

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | n/a
| License       | MIT
| Doc PR        | n/a

Commits
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26482d7 [Messenger] Add existing tags to unused whitelist

Author: Robin Chalas

src/Symfony/Bundle/FrameworkBundle/DependencyInjection/Compiler/UnusedTagsPass.php

@@ -39,6 +39,10 @@ class UnusedTagsPass implements CompilerPassInterface
         'kernel.event_listener',
         'kernel.event_subscriber',
         'kernel.fragment_renderer',
+        'messenger.bus',
+        'messenger.sender',
+        'messenger.receiver',
+        'messenger.message_handler',
         'monolog.logger',
         'routing.expression_language_provider',
         'routing.loader',