harden cache expiration test

In the worst case when the process sleeps for exactly one second the
current timestamp would be exactly the same as the expiration time.
Increasing the sleep time ensures that the tested item is always expired
when executing the test.

Author: xabbuh

src/Symfony/Component/Cache/Tests/Adapter/ProxyAdapterAndRedisAdapterTest.php

@@ -66,6 +66,7 @@ static function (CacheItem $item, $expiry) {
         $this->assertSame($value, $this->cache->getItem('baz')->get());
 
         sleep(1);
+        usleep(100000);
         $this->assertSame($value, $this->cache->getItem('foo')->get());
         $this->assertSame($value, $this->cache->getItem('bar')->get());
         $this->assertFalse($this->cache->getItem('baz')->isHit());