test: update snapshot tests

Author: ugur-vaadin

packages/dashboard/test/dom/__snapshots__/dashboard-layout.test.snap.js

@@ -2,7 +2,7 @@
 export const snapshots = {};
 
 snapshots["vaadin-dashboard-layout host"] = 
-`<vaadin-dashboard-layout>
+`<vaadin-dashboard-layout root-heading-level="2">
 </vaadin-dashboard-layout>
 `;
 /* end snapshot vaadin-dashboard-layout host */

packages/dashboard/test/dom/__snapshots__/dashboard.test.snap.js

@@ -2,7 +2,10 @@
 export const snapshots = {};
 
 snapshots["vaadin-dashboard host"] = 
-`<vaadin-dashboard style="">
+`<vaadin-dashboard
+  root-heading-level="2"
+  style=""
+>
   <vaadin-dashboard-widget-wrapper
     slot="slot-0"
     style=""