Add PHPUnit annotation.

This test performs an action which affects the global space of the test process, therefor, these
tests must run in separate PHP processes.

tests/Symfony/Tests/Component/Form/Extension/Csrf/CsrfProvider/DefaultCsrfProviderTest.php

@@ -13,6 +13,9 @@ namespace Symfony\Tests\Component\Form\Extension\Csrf\CsrfProvider;
 
 use Symfony\Component\Form\Extension\Csrf\CsrfProvider\DefaultCsrfProvider;
 
+/**
+ * @runTestsInSeparateProcesses
+ */
 class DefaultCsrfProviderTest extends \PHPUnit_Framework_TestCase
 {
     protected $provider;