PB-500 static test fix

Author: paras89

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

@@ -196,8 +196,16 @@
     box-shadow: @pagebuilder-affordance-box-shadow; // #ebebeb
     padding: 0;
 
-    &:not(.pagebuilder-column):not(.pagebuilder-column-group):before {
-        display: none;
+    &:not(
+    .pagebuilder-column,
+    ) {
+        &:not(
+        .pagebuilder-column-group
+        ){
+            &:before {
+                display: none;
+            }
+        }
     }
 
     > .pagebuilder-content-type.type-container.pagebuilder-row {