Update to django 4.1

[richardebeling]

(#1794 is currently blocked by a bug that is fixed in django 4.1)

Same procedure as every year

Some points I think might be relevant

• Django enables the cached template loader by default now. I think we want to be able to edit a template, reload the page, and instantly see the changes reflected with a development setup. So, we probably want to set a custom, non-cached template loader when DEBUG=True? Edit: As pointed out by @karyon below, the cached template loader has some auto-reload functionality, should work for us.
• https://code.djangoproject.com/ticket/33631 was closed, so blocktranslate asvar now marks the output as safe. This should allow us to remove all |safe filter calls that we have left in our templates after Fix broken html escaping in various places #1737. Edit: This will be in 4.2, not 4.1
• Django defaults to a new forms renderer using div tags. We should check if this breaks some layout because CSS rules do not apply anymore. Edit: As @karyon points out below, default will be changed in 5.0.

[karyon]

Regarding the first point, looking at https://code.djangoproject.com/ticket/33639, it seems that templates do auto-reload even when cached.
Regarding the third point, the default is changed only in 5.0.

Now that constraints are validated during model validation, this Questionnaire validation error can probably be expressed as a constraint. That would give us additional safety at the db level.

Somewhat related, I noticed a couple asserts/checks that might be better expressed as constraints. I'm not sure there was a reason why we didn't do that.

• start date must be before end date
• text and heading questions do not allow additional textanswers
• TextAnswer's answer and original_answer must not be the same
• Evaluation's _voter_count must be set iff _participant_count is set
• A bunch of validation when redeeming points