Bump mkdocs from 1.4.2 to 1.4.3 in /docs/user

Bumps [mkdocs](https://github.com/mkdocs/mkdocs) from 1.4.2 to 1.4.3.
- [Release notes](https://github.com/mkdocs/mkdocs/releases)
- [Commits](mkdocs/mkdocs@1.4.2...1.4.3)

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

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

docs/user/requirements.txt

@@ -1,4 +1,4 @@
-mkdocs==1.4.2
+mkdocs==1.4.3
 mkdocs-material==9.1.9
 mkdocstrings[python]==0.21.2
 mkdocstrings-python==0.9.0