Bump celery from 4.4.2 to 5.2.2

Bumps [celery](https://github.com/celery/celery) from 4.4.2 to 5.2.2.
- [Release notes](https://github.com/celery/celery/releases)
- [Changelog](https://github.com/celery/celery/blob/master/Changelog.rst)
- [Commits](celery/celery@4.4.2...v5.2.2)

---
updated-dependencies:
- dependency-name: celery
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

requirements.txt

@@ -30,7 +30,7 @@ geographiclib==1.52
 geopy==2.2.0
 # install ffmpeg on server
 python-ffmpeg-video-streaming==0.1.5
-celery==4.4.2
+celery==5.2.2
 # install redis-server on server
 redis==3.5.2
 wagtail==2.9