PB-500 mftf test fix

Author: paras89

app/code/Magento/PageBuilder/view/adminhtml/web/css/source/content-type/_preview.less

@@ -196,12 +196,8 @@
     box-shadow: @pagebuilder-affordance-box-shadow; // #ebebeb
     padding: 0;
 
-    &:not(
-    .pagebuilder-column,
-    .pagebuilder-column-group) {
-        &:before {
-            display: none;
-        }
+    &:not(.pagebuilder-column):not(.pagebuilder-column-group):before {
+        display: none;
     }
 
     > .pagebuilder-content-type.type-container.pagebuilder-row {