Merge pull request rails#47998 from p8/guides/index-headings

Fix headings in guides index [ci-skip]

Author: p8

guides/source/_welcome.html.erb

@@ -1,4 +1,4 @@
-<h2>Ruby on Rails Guides (<%= @edge ? @edge[0, 7] : @version %>)</h2>
+<h1>Ruby on Rails Guides (<%= @edge ? @edge[0, 7] : @version %>)</h1>
 
 <% if @edge %>
 <p>

guides/source/index.html.erb

@@ -18,7 +18,7 @@
 <% end %>
 
 <% documents_by_section.each do |section| %>
-  <h3><%= section['name'] %></h3>
+  <h2><%= section['name'] %></h2>
   <dl>
     <% section['documents'].each do |document| %>
       <%= guide(document['name'], document['url'], work_in_progress: document['work_in_progress']) do %>