Bump gunicorn from 21.2.0 to 23.0.0 in /server (#220)

Bumps [gunicorn](https://github.com/benoitc/gunicorn) from 21.2.0 to 23.0.0.
- [Release notes](https://github.com/benoitc/gunicorn/releases)
- [Commits](benoitc/gunicorn@21.2.0...23.0.0)

---
updated-dependencies:
- dependency-name: gunicorn
  dependency-type: direct:production
  update-type: version-update:semver-major
...

server/requirements.txt

@@ -35,7 +35,7 @@ websockets==13.*
 
 # deploy
 psycopg2==2.9.9
-gunicorn==21.2.0
+gunicorn==23.0.0
 uvicorn[standard]==0.30.6
 
 # dev