Toctree `numbered` option doesn't create <ol> element

Describe the bug When building HTML, the toctree numbered option doesn't create <ol> element but instead, keeps an <ul> and add a number to the title of the linked pages.

To Reproduce

.. toctree::
   :maxdepth: 1
   :numbered:

   page1.rst
   page2.rst

Gives

<ul>
<li class="toctree-l1"><a href="page1.html">1. My title</a></li>
<li class="toctree-l1"><a href="page2.html">2. My other title</a></li>
</ul>

That also creates styling problems like have a bullet in front of numbers.

Expected behavior

Semantically, wouldn't it be better to get:

<ol>
<li class="toctree-l1"><a href="page1.html">1. My title</a></li>
<li class="toctree-l1"><a href="page2.html">2. My other title</a></li>
</ol>

Environment info

• OS: macos
• Python version: 3.7.5
• Sphinx version: 3.1.1