Bump gunicorn from 21.2.0 to 22.0.0 in /backend/src in the pip group

Bumps the pip group in /backend/src with 1 update: [gunicorn](https://github.com/benoitc/gunicorn).


Updates `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
  dependency-group: pip
...

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

Author: dependabot[bot]

backend/src/requirements.txt

@@ -5,4 +5,4 @@ itsdangerous==2.1.2
 Jinja2==3.1.3
 MarkupSafe==2.1.5
 Werkzeug==3.0.2
-gunicorn==21.2.0
+gunicorn==22.0.0