Bump gunicorn from 22.0.0 to 23.0.0 in /backend/src

Bumps [gunicorn](https://github.com/benoitc/gunicorn) from 22.0.0 to 23.0.0.
- [Release notes](https://github.com/benoitc/gunicorn/releases)
- [Commits](benoitc/gunicorn@22.0.0...23.0.0)

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

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

backend/src/requirements.txt

@@ -5,4 +5,4 @@ itsdangerous==2.2.0
 Jinja2==3.1.4
 MarkupSafe==2.1.5
 Werkzeug==3.0.3
-gunicorn==22.0.0
+gunicorn==23.0.0