minor #34264 [VarDumper] Mark StubCaster as @final (fancyweb)

This PR was merged into the 4.4 branch.

Discussion
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[VarDumper] Mark StubCaster as @final

| Q             | A
| ------------- | ---
| Branch?       | 4.4
| Bug fix?      | no
| New feature?  |
| Deprecations? | yes
| Tickets       | -
| License       | MIT
| Doc PR        | -

Looks like it was forgotten in https://github.com/symfony/symfony/pull/33882.

@lyrixx was it intentional?

Commits
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d25b60961f [VarDumper] Mark StubCaster as @final

src/Symfony/Component/VarDumper/Caster/StubCaster.php

@@ -17,6 +17,8 @@ use Symfony\Component\VarDumper\Cloner\Stub;
  * Casts a caster's Stub.
  *
  * @author Nicolas Grekas <p@tchwork.com>
+ *
+ * @final since Symfony 4.4
  */
 class StubCaster
 {