chore(deps): bump gunicorn from 21.2.0 to 22.0.0 in /backend

Bumps [gunicorn](https://github.com/benoitc/gunicorn) from 21.2.0 to 22.0.0.
- [Release notes](https://github.com/benoitc/gunicorn/releases)
- [Commits](benoitc/gunicorn@21.2.0...22.0.0)

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

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

backend/requirements.txt

@@ -35,7 +35,7 @@ djangorestframework-simplejwt==5.3.1
     # via -r requirements.in
 drf-writable-nested==0.7.0
     # via -r requirements.in
-gunicorn==21.2.0
+gunicorn==22.0.0
     # via -r requirements.in
 markdown==3.6
     # via -r requirements.in