Fix deprecation: Added support for transitional form renderer

[matthewhegarty]

Problem

Fixes #1449. This affects the example application only.

There is a form template in the test app (category_list.html). This uses a {{ form }} tag. For django 4.1 this means that there has to be a declaration of the form renderer to use.

Solution

This change adds a conditional FormRenderer to test settings when the Django version is 4.1.

Acceptance Criteria

• Ran unit tests
• Manually checked the HTML rendering of http://localhost:8000/export/category/ before and after the addition of the setting. The form still renders ok.

form_after.html.txt
form_before.html.txt

[coveralls]

Coverage remained the same at 98.394% when pulling 8c023f4 on matthewhegarty:issue-1449-transitional-renderer into 033f803 on django-import-export:main.

[pokken-magic]

This looks sensible to me. Thanks.

[manelclos]

All good, thanks!