MQE-579: waitForLoadingMaskToDisappear fails sometimes when two loading masks match the same selector

- Added parenthesis according to the AC.

Author: KevinBKozan

src/Magento/FunctionalTestingFramework/Module/MagentoWebDriver.php

@@ -204,9 +204,13 @@ public function waitForPageLoad($timeout = 15)
     public function waitForLoadingMaskToDisappear()
     {
         foreach( self::$loadingMasksLocators as $maskLocator) {
+            // Get count of elements found for looping.
+            // Elements are NOT useful for interaction, as they cannot be fed to codeception actions.
             $loadingMaskElements = $this->_findElements($maskLocator);
             for ($i = 1; $i <= count($loadingMaskElements); $i++) {
-                $this->waitForElementNotVisible("{$maskLocator}[{$i}]", 30);
+                // Formatting and looping on i as we can't interact elements returned above
+                // eg.  (//div[@data-role="spinner"])[1]
+                $this->waitForElementNotVisible("({$maskLocator})[{$i}]", 30);
             }
         }
     }