Bump celery from 4.4.7 to 5.0.4 (#418)

Bumps [celery](https://github.com/celery/celery) from 4.4.7 to 5.0.4.
- [Release notes](https://github.com/celery/celery/releases)
- [Changelog](https://github.com/celery/celery/blob/master/Changelog.rst)
- [Commits](celery/celery@v4.4.7...v5.0.4)

Signed-off-by: dependabot-preview[bot] <[email protected]>

Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

Author: dependabot-preview[bot]

requirements.txt

@@ -3,5 +3,5 @@ aiohttp==3.7.2
 gidgethub==4.1.1
 cachetools==4.1.1
 redis==3.5.3
-celery==4.4.7
+celery==5.0.4
 sentry-sdk==0.17.3