provide tests for wrong dict access of admin class not raising TypeError

[benzkji]

this is the cause for #745 and #748. I don't have a solution (yet).

[benzkji]

This PR shows how dict access of a admin class that inherits from a TranslationAdmin is possible, and doesn't throw any error.

The dict access (which should raise a TypeError) returns the class itself, which leads to the errors in django-cms (caused by how the template system accesses data, see https://github.com/django/django/blob/main/django/template/base.py#L886, where first, dict access is tried, and not getattr afterwards, if this is successful).

[last-partizan]

Thanks, closing this PR.

I will use your code as a base for a proper test and fix.