minor #20969 [Security] Fix test (nicolas-grekas)

This PR was merged into the 2.8 branch.

Discussion
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[Security] Fix test

| Q             | A
| ------------- | ---
| Branch?       | 2.8
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

Commits
-------

8aeed88 [Security] Fix test

src/Symfony/Component/Security/Core/Tests/Authorization/Voter/AbstractVoterTest.php

@@ -122,7 +122,7 @@ class AbstractVoterTest extends \PHPUnit_Framework_TestCase
      */
     public function testSupportsAttribute($expected, $attribute, $message)
     {
-        $voter = new AbstractVoterTest_Voter();
+        $voter = new Fixtures\MyVoter();
 
         $this->assertEquals($expected, $voter->supportsAttribute($attribute), $message);
     }