minor symfony#28747 [Messenger] Remove forgotten experimental annotation in Doctrine bridge (Koc)

This PR was merged into the 4.2-dev branch.

Discussion
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[Messenger] Remove forgotten experimental annotation in Doctrine bridge

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no     <!-- see https://symfony.com/bc -->
| Deprecations? | no <!-- don't forget to update UPGRADE-*.md and src/**/CHANGELOG.md files -->
| Tests pass?   | yes    <!-- please add some, will be required by reviewers -->
| Fixed tickets |  -
| License       | MIT
| Doc PR        |  -

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Follow up of symfony#28406

Commits
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fe54a3e Remove forgotten experimental annotation in Doctrine bridge

Author: ogizanagi

src/Symfony/Bridge/Doctrine/Messenger/DoctrineTransactionMiddlewareFactory.php

@@ -18,7 +18,6 @@
  *
  * @author Maxime Steinhausser <maxime.steinhausser@gmail.com>
  *
- * @experimental in 4.1
  * @final
  */
 class DoctrineTransactionMiddlewareFactory