Use HTML beautifier to indent ERB files

We had inconsistent indentation in many places. Now we're fixing them
and adding a linter to our CI so we don't accidentally introduce
inconsistent indentations again.

app/views/admin/poll/polls/_poll_header.html.erb

@@ -19,8 +19,8 @@
     <div class="inline-block margin-left">
       <strong><%= t("admin.polls.index.geozone_restricted") %></strong>
       <br>
-        <%= @poll.geozones.pluck(:name).to_sentence %>
-      </div>
+      <%= @poll.geozones.pluck(:name).to_sentence %>
+    </div>
   <% end %>
 </div>