Add delay to the unstable test (#11538)

* Add delay to the unstable test

uitest/src/test/java/com/vaadin/tests/components/MenuBarDownloadBrowserOpenerUITest.java

@@ -30,6 +30,7 @@ public class MenuBarDownloadBrowserOpenerUITest extends MultiBrowserTest {
         checkAndCloseAlert();
         checkAndCloseAlert();
 
+        sleep(500);
         first.clickItem("TestExtension", "RemoveTrigger");
         first.clickItem("TestExtension", "RunMe");
         checkAndCloseAlert();

uitest/src/test/java/com/vaadin/tests/components/window/WindowHeaderButtonKeyboardActionsTest.java

@@ -400,6 +400,6 @@ public class WindowHeaderButtonKeyboardActionsTest extends MultiBrowserTest {
 
     protected void pressKeyAndWait(Keys... key) {
         new Actions(driver).sendKeys(key).build().perform();
-        sleep(100);
+        sleep(1000);
     }
 }