fix runtime cmp table header

Author: s7tya

site/frontend/src/pages/compare/runtime/comparisons-table.vue

@@ -50,6 +50,7 @@ const unit = computed(() => {
     <table v-else class="benches compare">
       <thead>
         <tr>
+          <th class="toggle-arrow"></th>
           <th>Benchmark</th>
           <th>% Change</th>
           <th>