fixes #15830: properly reset border-radius on list items in collapsing panel groups

less/panels.less

@@ -76,6 +76,7 @@
         .border-top-radius((@panel-border-radius - 1));
       }
     }
+
     // Add border bottom radius for last one
     &:last-child {
       .list-group-item:last-child {
@@ -84,6 +85,11 @@
       }
     }
   }
+  > .panel-heading + .panel-collapse > .list-group {
+    .list-group-item:first-child {
+      .border-top-radius(0);
+    }
+  }
 }
 // Collapse space between when there's no additional content.
 .panel-heading + .list-group {