avoid test suites failed with Fatal error when sockets extension is not available

tests/Monolog/Handler/UdpSocketTest.php

@@ -4,6 +4,9 @@ namespace Monolog\Handler;
 
 use Monolog\TestCase;
 
+/**
+ * @requires extension sockets
+ */
 class UdpSocketTest extends TestCase
 {
     public function testWeDoNotSplitShortMessages()