minor #29955 [Security] use final annotation to allow mocking the class (xabbuh)

This PR was merged into the 3.4 branch.

Discussion
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[Security] use final annotation to allow mocking the class

| Q             | A
| ------------- | ---
| Branch?       | 3.4
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #29946
| License       | MIT
| Doc PR        |

When the class was initially marked as `final`, it did only contain constants. Since #24337 the `Security` class also contains useful shortcut methods so allowing developers to mock the class in tests looks reasonable to me.

Commits
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1da00db247 use final annotation to allow mocking the class

src/Symfony/Component/Security/Core/Security.php

@@ -17,8 +17,10 @@ use Symfony\Component\Security\Core\User\UserInterface;
 
 /**
  * Helper class for commonly-needed security tasks.
+ *
+ * @final
  */
-final class Security
+class Security
 {
     const ACCESS_DENIED_ERROR = '_security.403_error';
     const AUTHENTICATION_ERROR = '_security.last_error';