Bump urllib3 from 1.26.17 to 1.26.18 in /requirements

Bumps [urllib3](https://github.com/urllib3/urllib3) from 1.26.17 to 1.26.18.
- [Release notes](https://github.com/urllib3/urllib3/releases)
- [Changelog](https://github.com/urllib3/urllib3/blob/main/CHANGES.rst)
- [Commits](https://github.com/urllib3/urllib3/compare/1.26.17...1.26.18)

---
updated-dependencies:
- dependency-name: urllib3
  dependency-type: indirect
...
Signed-off-by: dependabot[bot] <support@github.com>

requirements/checkdocs.txt

@@ -103,7 +103,7 @@ tornado==6.3.3
     # via livereload
 typing-extensions==4.3.0
     # via myst-parser
-urllib3==1.26.17
+urllib3==1.26.18
     # via requests
 wheel==0.38.1
     # via pip-tools

requirements/docs.txt

@@ -103,7 +103,7 @@ tornado==6.3.3
     # via livereload
 typing-extensions==4.3.0
     # via myst-parser
-urllib3==1.26.17
+urllib3==1.26.18
     # via requests
 wheel==0.38.1
     # via pip-tools