Bump gunicorn from 21.2.0 to 22.0.0 in /backend (#1176)

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
...

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Author: dependabot[bot]

backend/poetry.lock

@@ -15,7 +15,7 @@ tenacity = "^8.2.3"
 pydantic = ">2.0"
 emails = "^0.6"
 
-gunicorn = "^21.2.0"
+gunicorn = "^22.0.0"
 jinja2 = "^3.1.2"
 alembic = "^1.12.1"
 python-jose = {extras = ["cryptography"], version = "^3.3.0"}