Fix download.html (GH-18902)

`<tt>` is not allowed.

Co-authored-by: Kyle Stanley <[email protected]>

Author: methane

Doc/tools/templates/download.html

@@ -40,7 +40,7 @@ <h1>Download Python {{ release }} Documentation</h1>
 
 <p>These archives contain all the content in the documentation.</p>
 
-<p>HTML Help (<tt>.chm</tt>) files are made available in the "Windows" section
+<p>HTML Help (<code>.chm</code>) files are made available in the "Windows" section
 on the <a href="https://www.python.org/downloads/release/python-{{ release.replace('.', '') }}/">Python
 download page</a>.</p>