Bump gunicorn from 19.9.0 to 22.0.0 in /utils/google_app_engine

Bumps [gunicorn](https://github.com/benoitc/gunicorn) from 19.9.0 to 22.0.0.
- [Release notes](https://github.com/benoitc/gunicorn/releases)
- [Commits](benoitc/gunicorn@19.9.0...22.0.0)

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

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

utils/google_app_engine/additional_requirements.txt

@@ -1,4 +1,4 @@
 # add these requirements in your app on top of the existing ones
 pip==21.1
 Flask==1.0.2
-gunicorn==19.9.0
+gunicorn==22.0.0