Add test

Signed-off-by: Petr Shumilov <p.shumilov@vkteam.ru>

Author: PetrShumilov

tests/phpt/fork/043_sched_yield_in_callback.php

@@ -0,0 +1,21 @@
+@ok
+<?php
+require_once 'kphp_tester_include.php';
+
+/**
+ * @kphp-required
+ * @param int $a
+ * @param int $b
+ * @return int
+ */
+function cmp(int $a, int $b) {
+#ifndef KPHP
+  sched_yield();
+#endif
+  return $b - $a;
+}
+function main() {
+  $arr = [3, 2, 1];
+  uasort($arr, 'cmp');
+}
+main();