See context here: https://django-ratelimit.readthedocs.io/en/latest/cookbook/429.html#context
For now we continue to fall back to django's default 403 handler for 403
but provide a new 429 template that we use for ratelimit exceptions.
This commit also updates a logistration test that relied on the old 403
behavior of django-ratelimit instead of the newly added 429 behavior.
