Add an aria-label to the "choose your booth" select

We're using the `aria-label` attribute instead of a label because this
is a page where only one field is rendered and the text of the label is
the same as the text of the <h1> tag.

We're using `aria-label` instead of `aria-labelledby` because the former
is supported by Capybara.

app/views/officing/booth/new.html.erb

@@ -12,8 +12,8 @@
           <div class="small-12 column">
             <%= f.select :id,
                          @booths.map { |booth| [booth.location, booth.id] },
-                         selected: @booths.first,
-                         label: false %>
+                         { selected: @booths.first, label: false },
+                         { "aria-label": t("officing.booth.new.title") } %>
 
             <%= f.submit(t("devise_views.sessions.new.submit"), class: "button expanded") %>
           </div>