fix: requirements.txt to reduce vulnerabilities

The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-CERTIFI-3164749
- https://snyk.io/vuln/SNYK-PYTHON-CERTIFI-5805047
- https://snyk.io/vuln/SNYK-PYTHON-CERTIFI-7430173
- https://snyk.io/vuln/SNYK-PYTHON-IDNA-6597975
- https://snyk.io/vuln/SNYK-PYTHON-REQUESTS-5595532

Author: snyk-bot

requirements.txt

@@ -29,4 +29,6 @@ pymdown-extensions>=9.9.1
 # Requirements for plugins
 colorama>=0.4
 regex>=2022.4.24
-requests>=2.26
+requests>=2.31.0
+certifi>=2024.7.4 # not directly required, pinned by Snyk to avoid a vulnerability
+idna>=3.7 # not directly required, pinned by Snyk to avoid a vulnerability