Use of Django ugettext_lazy breaks with Django 4+

[chosak]

This project uses Django's ugettext_lazy method in several places. ugettext_lazy was deprecated in Django 3.0 and removed in Django 4.0.

This project doesn't specify a particular pinned range for Django in its setup.py (although it does for testing). This causes a failure unless you pin Django < 4:

% pip install wagtail-treemodeladmin
% pip freeze | grep Django==
Django==4.0.8
% pip freeze | grep wagtail==
wagtail==2.16.3
% wagtail start myproject
% cd myproject
# Edit myproject/settings/base.py to add 'treemodeladmin' to INSTALLED_APPS
% ./manage.py migrate
...
    from django.utils.translation import ugettext_lazy as _
ImportError: cannot import name 'ugettext_lazy' from 'django.utils.translation'

[willbarton]

Good catch, thanks! I've replaced ugettext in df3a0a7 in #34.