Moved from ugettext(_lazy) to gettext(_lazy).

[facundobatista]

This is to avoid zillion messages like this when running tests:

/home/runner/work/pyarweb/pyarweb/events/models.py:50: RemovedInDjango40Warning: django.utils.translation.ugettext_lazy() is deprecated in favor of django.utils.translation.gettext_lazy().