fix: docs/requirements.txt to reduce vulnerabilities

The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-MKDOCSMATERIAL-7856160

docs/requirements.txt

@@ -1,5 +1,5 @@
 mkdocs==1.4.2
-mkdocs-material==9.0.5
+mkdocs-material==9.5.32
 pymdown-extensions>=9.9.1
 mkdocs_pymdownx_material_extras==2.3.1
 mkdocs-minify-plugin==0.6.2