MOBILE-3320 behat: Fix negated step

Author: NoelDeMartin

tests/behat/behat_app.php

@@ -683,7 +683,7 @@ public function the_header_should_be_in_the_app(string $text) {
      * @Given /^the app should( not)? have opened a browser tab$/
      * @param bool $not
      */
-    public function the_app_should_have_opened_a_browser_tab(bool $not) {
+    public function the_app_should_have_opened_a_browser_tab(bool $not = false) {
         $this->spin(function() use ($not) {
             $openedbrowsertab = count($this->getSession()->getWindowNames()) === 2;