minor #32382 Fix phpdocs (fabpot)

This PR was merged into the 4.4 branch.

Discussion
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Fix phpdocs

| Q             | A
| ------------- | ---
| Branch?       | 3.4
| Bug fix?      | no
| New feature?  | no <!-- please update src/**/CHANGELOG.md files -->
| BC breaks?    | no     <!-- see https://symfony.com/bc -->
| Deprecations? | no <!-- please update UPGRADE-*.md and src/**/CHANGELOG.md files -->
| Tests pass?   | yes    <!-- please add some, will be required by reviewers -->
| Fixed tickets | n/a
| License       | MIT
| Doc PR        | n/a

Backported from #32286

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Commits
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4acddef91b fixed phpdocs

Author: fabpot

Command/AbstractConfigCommand.php

@@ -52,6 +52,9 @@ protected function listBundles($output)
         }
     }
 
+    /**
+     * @return ExtensionInterface
+     */
     protected function findExtension($name)
     {
         $bundles = $this->initializeBundles();