Sanitize translations instead of using _html

Using the `_html` suffix in an i18n key is the same as using `html_safe`
on it, which means that translation could potentially be used for XSS
attacks.

app/views/shared/_errors.html.erb

@@ -10,7 +10,7 @@
       <% if local_assigns[:message].present? %>
         <%= message %>
       <% else %>
-        <%= t("form.not_saved_html", resource: t("form.#{resource.class.to_s.underscore}")) %>
+        <%= sanitize(t("form.not_saved", resource: t("form.#{resource.class.to_s.underscore}"))) %>
       <% end %>
     </strong>
   </div>