fix: requirements-dev.txt to reduce vulnerabilities (#6)

The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-REQUESTS-6928867

Co-authored-by: snyk-bot <[email protected]>

Author: westy92

requirements-dev.txt

@@ -1,3 +1,4 @@
 flake8>=5.0.4
 pytest-cov>=4.0.0
 requests-mock>=1.10.0
+requests>=2.32.0 # not directly required, pinned by Snyk to avoid a vulnerability