Bump mkdocs from 1.4.1 to 1.4.2 in /requirements.d

Bumps [mkdocs](https://github.com/mkdocs/mkdocs) from 1.4.1 to 1.4.2.
- [Release notes](https://github.com/mkdocs/mkdocs/releases)
- [Commits](mkdocs/mkdocs@1.4.1...1.4.2)

---
updated-dependencies:
- dependency-name: mkdocs
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

requirements.d/docs.txt

@@ -1,6 +1,6 @@
 # Requirements for [testenv:docs] virtualenv
 
 jinja2==3.0.3
-mkdocs==1.4.1
+mkdocs==1.4.2
 pymdown-extensions==9.1
 Pygments==2.11.2