Fix group names in lesson event description

aleksis/apps/chronos/templates/chronos/lesson_event_description.txt

-{% load i18n %}{% trans "Groups" %}: {{ event.group_names_with_amends|default:"–" }}{% if event.subject %}
+{% load i18n %}{% trans "Groups" %}: {{ event.group_names|default:"–" }}{% if event.subject %}
 {% trans "Subject" %}: {{ event.subject_name_with_amends }}{% endif %}
 {% trans "Teachers" %}: {{ event.teacher_names_with_amends|default:"–" }}
 {% trans "Rooms" %}: {{ event.room_names_with_amends|default:"–" }}{% if event.comment %}