fix: requirements_dev.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-JINJA2-6150717
- https://snyk.io/vuln/SNYK-PYTHON-PYGMENTS-1086606
- https://snyk.io/vuln/SNYK-PYTHON-PYGMENTS-5750273
- https://snyk.io/vuln/SNYK-PYTHON-REQUESTS-5595532
- https://snyk.io/vuln/SNYK-PYTHON-SETUPTOOLS-3180412
- https://snyk.io/vuln/SNYK-PYTHON-SPHINX-570772
- https://snyk.io/vuln/SNYK-PYTHON-SPHINX-570773
- https://snyk.io/vuln/SNYK-PYTHON-SPHINX-5811865
- https://snyk.io/vuln/SNYK-PYTHON-SPHINX-5812109

Author: snyk-bot

requirements_dev.txt

@@ -4,7 +4,7 @@ bump2version==1.0.*
 flake8==4.*
 coverage==6.*
 pytest>=5.3.5
-Sphinx==4.*
+Sphinx==3.3.0
 twine==3.*
 black==22.1.0
 pre-commit
@@ -14,4 +14,9 @@ isort
 pytest-benchmark
 pyte
 freezegun==1.*
-pexpect
+pexpect
+certifi>=2023.7.22 # not directly required, pinned by Snyk to avoid a vulnerability
+jinja2>=3.1.3 # not directly required, pinned by Snyk to avoid a vulnerability
+pygments>=2.15.0 # not directly required, pinned by Snyk to avoid a vulnerability
+requests>=2.31.0 # not directly required, pinned by Snyk to avoid a vulnerability
+setuptools>=65.5.1 # not directly required, pinned by Snyk to avoid a vulnerability