fix: requirements.txt to reduce vulnerabilities

The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-GUNICORN-6615672
- https://snyk.io/vuln/SNYK-PYTHON-URLLIB3-6002459
- https://snyk.io/vuln/SNYK-PYTHON-WERKZEUG-6035177
- https://snyk.io/vuln/SNYK-PYTHON-WERKZEUG-6808933

requirements.txt

@@ -4,7 +4,7 @@ click==8.1.3
 Flask==2.2.5
 Flask-Login==0.6.2
 Flask-SQLAlchemy==3.0.3
-gunicorn==20.1.0
+gunicorn==22.0.0
 idna==3.7
 importlib-metadata==6.0.0
 Jinja2==3.1.4
@@ -14,8 +14,8 @@ python-digitalocean==1.17.0
 requests==2.31.0
 SQLAlchemy==2.0.1
 typing_extensions==4.4.0
-urllib3==1.26.17
-Werkzeug==2.2.3
+urllib3==1.26.18
+Werkzeug==3.0.3
 wheel==0.38.0
 zipp==3.12.0
 setuptools>=65.5.1 # not directly required, pinned by Snyk to avoid a vulnerability