[tests] Require pcntl extension to run blocking PubSub\Consumer test.

tests/Predis/PubSub/ConsumerTest.php

@@ -343,6 +343,7 @@ class ConsumerTest extends PredisTestCase
 
     /**
      * @group connected
+     * @requires extension pcntl
      */
     public function testPubSubAgainstRedisServerBlocking()
     {