Update dependency Celery to v5

This MR contains the following updates:

Package	Type	Update	Change
Celery	dependencies	major	^4.4.0 -> ^5.0.0

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pyproject.toml

@@ -68,7 +68,7 @@ html2text = "^2020.0.0"
 django-ckeditor = "^6.0.0"
 django-js-reverse = "^0.9.1"
 calendarweek = "^0.4.3"
-Celery = {version="^4.4.0", optional=true, extras=["django", "redis"]}
+Celery = {version="^5.0.0", optional=true, extras=["django", "redis"]}
 django-celery-results = {version="^1.1.2", optional=true}
 django-celery-beat = {version="^2.0.0", optional=true}
 django-celery-email = {version="^3.0.0", optional=true}