minor #33857 [DI] Whitelist validator.auto_mapper in UnusedTagsPass (chalasr)

This PR was merged into the 4.3 branch.

Discussion
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[DI] Whitelist validator.auto_mapper in UnusedTagsPass

| Q             | A
| ------------- | ---
| Branch?       | 4.3
| Bug fix?      | no
| New feature?  | no
| Deprecations? | no
| Tickets       | -
| License       | MIT
| Doc PR        | -

Commits
-------

811758c [DI] Whitelist validator.auto_mapper in UnusedTagsPass

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

@@ -62,6 +62,7 @@ class UnusedTagsPass implements CompilerPassInterface
         'twig.loader',
         'validator.constraint_validator',
         'validator.initializer',
+        'validator.auto_mapper',
     ];
 
     public function process(ContainerBuilder $container)