Serve error page content with the same protocol as the page itself (fixe...

Related PRs to also merge:

  - `work4us`: https://github.com/Work4Labs/work4us/pull/6330
  - `django-short-urls`: https://github.com/olivierlefloch/django-short-urls/pull/25
  - `chef`: https://github.com/Work4Labs/Chef/pull/50