fix: requirements.txt to reduce vulnerabilities

The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-XML2RFC-12215106

Author: snyk-bot

requirements.txt

@@ -50,7 +50,7 @@ urllib3==1.26.18
     # via requests
 webencodings==0.5.1
     # via html5lib
-xml2rfc==3.12.4
+xml2rfc==3.30.1
     # via -r requirements.in
 
 # The following packages are considered to be unsafe in a requirements file: