Bump mkdocs from 1.5.2 to 1.5.3 in /docs

Bumps [mkdocs](https://github.com/mkdocs/mkdocs) from 1.5.2 to 1.5.3.
- [Release notes](https://github.com/mkdocs/mkdocs/releases)
- [Commits](mkdocs/mkdocs@1.5.2...1.5.3)

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

Signed-off-by: dependabot[bot] <[email protected]>

docs/requirements.txt

@@ -10,7 +10,7 @@ MarkupSafe==2.1.3
 mdx-truly-sane-lists==1.3
 mergedeep==1.3.4
 mike==1.1.2
-mkdocs==1.5.2
+mkdocs==1.5.3
 mkdocs-exclude==1.0.2
 mkdocs-macros-plugin==1.0.4
 mkdocs-material==9.3.1