Switch to <ol> for breadcrumb

The Breadcrumb Glossary page notes

> _Note: While there's no dedicated semantic HTML element for breadcrumb navigation menus, the <ol> element is commonly used to represent their hierarchical structure._

I suggest following our own advice. From a semantically standpoint, it just makes to use an ordered list.

files/en-us/web/css/layout_cookbook/breadcrumb_navigation/index.md

@@ -20,13 +20,13 @@ Click "Play" in the code blocks below to edit the example in the MDN Playground:
 
 ```html live-sample___breadcrumb-example
 <nav aria-label="Breadcrumb" class="breadcrumb">
-  <ul>
+  <ol>
     <li><a href="#">Home</a></li>
     <li><a href="#">Category</a></li>
     <li><a href="#">Sub Category</a></li>
     <li><a href="#">Type</a></li>
     <li><span aria-current="page">Product</span></li>
-  </ul>
+  </ol>
 </nav>
 ```