Bump gunicorn

Bumps [gunicorn](https://github.com/benoitc/gunicorn) from 20.1.0 to 22.0.0.
- [Release notes](https://github.com/benoitc/gunicorn/releases)
- [Commits](benoitc/gunicorn@20.1.0...22.0.0)

---
updated-dependencies:
- dependency-name: gunicorn
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

backstage-reference/templates/example-python-flask/content/requirements.txt

@@ -4,4 +4,4 @@ itsdangerous==2.1.2
 Jinja2==3.1.3
 MarkupSafe==2.1.2
 Werkzeug==2.3.8
-gunicorn==20.1.0
+gunicorn==22.0.0