Update horizon local settings for Django 4

As horizon is now using Django 4 after a recent requirements update, we
need to clean our config from settings that were long deprecated and now
no longer work.

[0] https://review.opendev.org/c/openstack/horizon/+/891828
[1] https://review.opendev.org/c/openstack/horizon/+/827092

Change-Id: I47533a2ad436578c98503284c25db4fd51896506

ansible/roles/horizon/templates/local_settings.j2

@@ -2,7 +2,7 @@
 
 import os
 
-from django.utils.translation import ugettext_lazy as _
+from django.utils.translation import gettext_lazy as _
 
 from openstack_dashboard import exceptions
 from openstack_dashboard.settings import HORIZON_CONFIG
@@ -178,7 +178,7 @@ SECRET_KEY='{{ horizon_secret_key }}'
 SESSION_ENGINE = 'django.contrib.sessions.backends.cache'
 CACHES = {
     'default': {
-        'BACKEND': 'django.core.cache.backends.memcached.MemcachedCache',
+        'BACKEND': 'django.core.cache.backends.memcached.PyMemcacheCache',
         'LOCATION': [{% for host in groups['memcached'] %}'{{ 'api' | kolla_address(host) | put_address_in_context('memcache') }}:{{ memcached_port }}'{% if not loop.last %},{% endif %}{% endfor %}]
     }
 }