Stop supporting celery 4

setup.py

@@ -23,7 +23,7 @@ def read(*parts):
 
 install_requires = [
     'Django>=3.2',
-    'celery>=4.0',
+    'celery>=5.0',
 ]
 
 setup(

tox.ini

@@ -10,11 +10,9 @@ deps =
     coverage
     django3: Django>=3.2,<4.0
     django4: Django>=4.0,<5.0
-    celery4: celery>=4.0,<5.0
-    celery5: celery>=5.0,<6.0
 commands =
     pip install -e .
     make test
 
 [tox]
-envlist = {py38,py39,py310}-django{3,4}-celery{4,5}
+envlist = {py38,py39,py310}-django{3,4}