[Snyk] Security upgrade gunicorn from 19.9.0 to 19.10.0 (#10933)

fix: utils/google_app_engine/additional_requirements.txt to reduce vulnerabilities


The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-GUNICORN-541164

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==19.10.0