dependency: (deps): bump tzdata from 2023.3 to 2023.4 in /backend

Bumps [tzdata](https://github.com/python/tzdata) from 2023.3 to 2023.4.
- [Release notes](https://github.com/python/tzdata/releases)
- [Changelog](https://github.com/python/tzdata/blob/master/NEWS.md)
- [Commits](python/tzdata@2023.3...2023.4)

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

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

backend/requirements.txt

@@ -4,4 +4,4 @@ djangorestframework==3.14.0
 pytz==2023.3.post1
 sqlparse==0.4.4
 typing_extensions==4.9.0
-tzdata==2023.3
+tzdata==2023.4