Bump gunicorn from 20.0.4 to 23.0.0 in /nginx-wsgi-flask/flask

Bumps [gunicorn](https://github.com/benoitc/gunicorn) from 20.0.4 to 23.0.0.
- [Release notes](https://github.com/benoitc/gunicorn/releases)
- [Commits](https://github.com/benoitc/gunicorn/compare/20.0.4...23.0.0)

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

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

nginx-wsgi-flask/flask/requirements.txt

@@ -1,2 +1,2 @@
 Flask==1.1.1
-gunicorn==20.0.4
+gunicorn==23.0.0