fix: days/97-99-online-game-api/demo_app/web/requirements.txt to reduce vulnerabilities

The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-WERKZEUG-3319935
- https://snyk.io/vuln/SNYK-PYTHON-WERKZEUG-3319936

Author: snyk-bot

days/97-99-online-game-api/demo_app/web/requirements.txt

@@ -1,2 +1,3 @@
 flask
-sqlalchemy
+sqlalchemy
+werkzeug>=2.2.3 # not directly required, pinned by Snyk to avoid a vulnerability