minor #16187 [2.8][tests] Use @requires annotation when possible (nicolas-grekas)

This PR was merged into the 2.8 branch.

Discussion
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[2.8][tests] Use @requires annotation when possible

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

Commits
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814d961 [tests] Use @requires annotation when possible

Author: nicolas-grekas

Tests/LdapClientTest.php

@@ -13,15 +13,11 @@
 
 use Symfony\Component\Ldap\LdapClient;
 
+/**
+ * @requires extension ldap
+ */
 class LdapClientTest extends \PHPUnit_Framework_TestCase
 {
-    protected function setUp()
-    {
-        if (!extension_loaded('ldap')) {
-            $this->markTestSkipped('The ldap extension is not available');
-        }
-    }
-
     /**
      * @dataProvider provideLdapEscapeValues
      */