Update tests for redis and email urls

[lilioid]

django-cache-url and dj-email-url recently partially changed their behavior.
We should update our tests to reflect the changes.

In detail, the following changes have been made:

• django-cache-url now uses djangos native redis backend for django>4
• dj-email-url added support for the EMAIL_TIMEOUT setting which defaults to None

[mgorny]

Ping.