Downgrade celery to 4.4.7

see celery/celery#6363

ansible/roles/celerybeat/templates/celerybeat.service.j2

@@ -7,8 +7,8 @@ Type=simple
 User=celery
 Group=celery
 WorkingDirectory={{ fdg_base_path }}/FahrplanDatenGarten
-ExecStart=/bin/sh -c '{{ celery_bin }} beat \
-  -A {{ celery_app }} --pidfile={{ celerybeat_pid_file }} \
+ExecStart=/bin/sh -c '{{ celery_bin }} -A {{ celery_app }}  beat \
+  --pidfile={{ celerybeat_pid_file }} \
   --logfile={{ celerybeat_log_file }} --loglevel={{ celerybeat_log_level }} {{ celerybeat_opts }}'
 
 [Install]

ansible/roles/worker_celery/templates/celeryd.service.j2

@@ -8,13 +8,14 @@ User=celery
 Group=celery
 Restart=always
 WorkingDirectory={{ fdg_base_path }}/FahrplanDatenGarten
+Environment="CELERY_APP={{ celery_app }}"
 ExecStart=/bin/sh -c '{{ celery_bin }} multi start {{ celeryd_nodes }} \
-  -A {{ celery_app }} --pidfile={{ celeryd_pid_file }} \
+  --pidfile={{ celeryd_pid_file }} \
   --logfile={{ celeryd_log_file }} --loglevel={{ celeryd_log_level }} {{ celeryd_opts }}'
 ExecStop=/bin/sh -c '{{ celery_bin }} multi stopwait {{ celeryd_nodes }} \
   --pidfile={{ celeryd_pid_file }}'
 ExecReload=/bin/sh -c '{{ celery_bin }} multi restart {{ celeryd_nodes }} \
-  -A {{ celery_app }} --pidfile={{ celeryd_pid_file }} \
+  --pidfile={{ celeryd_pid_file }} \
   --logfile={{ celeryd_log_file }} --loglevel={{ celeryd_log_level }} {{ celeryd_opts }}'
 
 [Install]

requirements.txt

@@ -1,10 +1,10 @@
-django~=3.1.1
+Django~=3.1.1
 requests~=2.24.0
 fdfgen~=0.16.1
 flake8~=3.8.3
 isort~=5.5.3
 pycryptodome~=3.9.8
-celery~=5.0.0
+celery~=4.4.7
 redis~=3.5.3
 pytz==2020.1
 psycopg2-binary~=2.8.6