fix: requirements.txt to reduce vulnerabilities

The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-DJANGO-7435780
- https://snyk.io/vuln/SNYK-PYTHON-DJANGO-7436273
- https://snyk.io/vuln/SNYK-PYTHON-DJANGO-7436514
- https://snyk.io/vuln/SNYK-PYTHON-DJANGO-7436646

Author: snyk-bot

requirements.txt

@@ -51,4 +51,5 @@ configobj
 boto3
 pandas
 pyperclip
-backports-datetime-fromisoformat; python_version < '3.11'
+backports-datetime-fromisoformat; python_version < '3.11'
+django>=4.2.14 # not directly required, pinned by Snyk to avoid a vulnerability