style: collapse borders of single list in section (#21838)

gadjo/static/css/gadjo.scss

@@ -1065,6 +1065,9 @@ div.section {
 			}
 		}
 	}
+	> div > ul.objects-list:first-child:last-child { // single child
+		margin: calc(-1rem - 1px);
+	}
 }
 
 @import 'grid';