Stabilize test case timings

Author: Vectorial1024

tests/AsyncTaskTest.php

@@ -141,9 +141,10 @@ public function testAsyncTimeout()
         $task = new AsyncTask($timeoutTask);
         $task->withTimeLimit(1)->start();
         // we wait for it to timeout
-        $this->sleep(0.5);
-        $this->sleep(0.5);
-        $this->sleep(0.5);
+        $this->sleep(0.4);
+        $this->sleep(0.4);
+        $this->sleep(0.4);
+        $this->sleep(0.4);
         // should have timed out
         $this->assertFileExists($textFilePath, "The async task probably did not trigger its timeout handler because its timeout output file is not found.");
         $this->assertStringEqualsFile($textFilePath, $message);