build(deps): bump python-dateutil from 2.8.2 to 2.9.0.post0 in /backend

Bumps [python-dateutil](https://github.com/dateutil/dateutil) from 2.8.2 to 2.9.0.post0.
- [Release notes](https://github.com/dateutil/dateutil/releases)
- [Changelog](https://github.com/dateutil/dateutil/blob/master/NEWS)
- [Commits](dateutil/dateutil@2.8.2...2.9.0.post0)

---
updated-dependencies:
- dependency-name: python-dateutil
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

backend/requirements.txt

@@ -6,7 +6,7 @@ Flask-Cors==4.0.1
 flask-talisman==1.1.0
 google-cloud-storage==2.16.0
 gunicorn==22.0.0
-python-dateutil==2.8.2
+python-dateutil==2.9.0.post0
 pytoml==0.1.21
 redis==5.0.4
 swagger-ui-bundle==1.1.0