build(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] <[email protected]>

Author: dependabot[bot]

backend/requirements.txt

@@ -5,7 +5,7 @@ Flask==2.2.3
 Flask-Cors==4.0.0
 flask-talisman==1.1.0
 google-cloud-storage==2.14.0
-gunicorn==21.2.0
+gunicorn==22.0.0
 python-dateutil==2.8.2
 pytoml==0.1.21
 redis==5.0.1