build(deps): Bump mkdocs from 1.3.1 to 1.4.0

Bumps [mkdocs](https://github.com/mkdocs/mkdocs) from 1.3.1 to 1.4.0.
- [Release notes](https://github.com/mkdocs/mkdocs/releases)
- [Commits](mkdocs/mkdocs@1.3.1...1.4.0)

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

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

requirements.txt

@@ -1,4 +1,4 @@
-mkdocs==1.3.1
+mkdocs==1.4.0
 mike==1.1.2
 markdown==3.3.7 # Temporarily pin version <3.4, see https://github.com/mkdocs/mkdocs/pull/2893
 mkdocs-material==8.2.3