update celery to 4.4.0 to fix python 3.7 issue

[androolloyd]

Description

Bump celery version

Refers/Fixes

Issue with python 3.7 and the async keyword

celery/celery#4849

[codecov]

Codecov Report

Merging #5755 into stable will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           stable    #5755   +/-   ##
=======================================
  Coverage   29.87%   29.87%           
=======================================
  Files         257      257           
  Lines       21809    21809           
  Branches     3170     3170           
=======================================
  Hits         6515     6515           
+ Misses      15017    15014    -3     
- Partials      277      280    +3

Impacted Files	Coverage Δ
app/dashboard/views.py	11.97% <0%> (ø)	⬆️
...rketing/management/commands/no_applicants_email.py	0% <0%> (ø)	⬆️

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