Update gunicorn requirement from ==20.1.* to ==22.0.* in /requirements

Updates the requirements on [gunicorn](https://github.com/benoitc/gunicorn) to permit the latest version.
- [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>

requirements/production.txt

@@ -3,7 +3,7 @@
 -r ./base.txt
 
 # Using gunicorn (and probably nginx)
-gunicorn==20.1.*  # https://github.com/benoitc/gunicorn
+gunicorn==22.0.*  # https://github.com/benoitc/gunicorn
 
 
 # PostgreSQL driver