MC-23059: Template strict mode is not set for unsaved template previews

Author: nathanjosiah

app/code/Magento/Newsletter/Test/Mftf/ActionGroup/AdminNewsletterTemplateActionGroup.xml

@@ -34,11 +34,11 @@
         <waitForElementVisible selector="{{BasicFieldNewsletterSection.templateName}}" stepKey="waitForPreviewButton"/>
         <click selector="{{BasicFieldNewsletterSection.preview}}" stepKey="clickPreview"/>
         <switchToNextTab stepKey="switchToPreviewTab"/>
+        <waitForLoadingMaskToDisappear stepKey="waitForLoadingMask"/>
         <waitForElementVisible selector="{{BasicFieldNewsletterSection.previewIframe}}" stepKey="waitForIframeVisible"/>
         <executeJS function="document.getElementById('preview_iframe').sandbox.add('allow-scripts')" stepKey="addSandboxValue"/>
-        <wait time="10" stepKey="waitForSandbox"/>
         <switchToIFrame userInput="preview_iframe" stepKey="switchToIframe"/>
-        <waitForPageLoad stepKey="waitForPreviewIframeLoaded"/>
+        <waitForElementVisible selector="body" stepKey="waitForIframeLoad"/>
     </actionGroup>
 
     <actionGroup name="AdminAssertNewsletterContent">