Bump urllib3 from 2.0.4 to 2.0.6 in /doc

Bumps [urllib3](https://github.com/urllib3/urllib3) from 2.0.4 to 2.0.6.
- [Release notes](https://github.com/urllib3/urllib3/releases)
- [Changelog](https://github.com/urllib3/urllib3/blob/main/CHANGES.rst)
- [Commits](urllib3/urllib3@2.0.4...2.0.6)

---
updated-dependencies:
- dependency-name: urllib3
  dependency-type: direct:production
...

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

doc/requirements.txt

@@ -29,4 +29,4 @@ sphinxcontrib-jquery==4.1
 sphinxcontrib-jsmath==1.0.1
 sphinxcontrib-qthelp==1.0.6
 sphinxcontrib-serializinghtml==1.1.9
-urllib3==2.0.4
+urllib3==2.0.6