style(toc): update icon color from yellow to red

src/styles/post-toc.scss

@@ -104,7 +104,7 @@
   // 标签图标 <>
   &__icon {
     flex-shrink: 0;
-    color: var(--yellow);
+    color: var(--red);
     margin-right: 4px;
     opacity: 0.7;
   }