fix: requirements.txt to reduce vulnerabilities

The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-ZIPP-7430899

Author: snyk-bot

requirements.txt

@@ -16,4 +16,5 @@ pytest-cov==2.12.1
 python-dateutil==2.8.2
 python-dotenv==0.19.0
 psycopg2-binary==2.9.1
-better-profanity==0.7.0
+better-profanity==0.7.0
+zipp>=3.19.1 # not directly required, pinned by Snyk to avoid a vulnerability