Add banner role to logo container in sidebar header

All page content must be contained by landmarks: https://dequeuniversity.com/rules/axe/4.1/region

Author: barrymcgee

includes/header.html

@@ -5,7 +5,7 @@
 
   <header class="container-xl px-3 px-md-6 pt-3 pb-2 position-relative d-flex flex-justify-between width-full {% if error == '404' %} d-md-none {% endif %}">
 
-    <div class="d-flex flex-items-center d-lg-none" style="z-index: 3;" id="github-logo-mobile">
+    <div class="d-flex flex-items-center d-lg-none" style="z-index: 3;" id="github-logo-mobile" role="banner">
       <a href="/{{ currentLanguage }}" aria-hidden="true" tabindex="-1">
         {% octicon "mark-github" height="32" class="text-black" %}
       </a>

includes/sidebar.html

@@ -1,7 +1,7 @@
 <!-- product > category > maptopic > article -->
 <div class="sidebar d-none d-lg-block">
 
-  <div class="d-flex flex-items-center p-4 position-sticky top-0 sidebar-background-color" style="z-index: 3;" id="github-logo">
+  <div class="d-flex flex-items-center p-4 position-sticky top-0 sidebar-background-color" style="z-index: 3;" id="github-logo" role="banner">
     <a href="/{{ currentLanguage }}" class="text-white" aria-hidden="true" tabindex="-1">
       {% octicon "mark-github" height="32" %}
     </a>