build(deps): bump urllib3 from 1.26.3 to 1.26.4 in /docs (#238)

Bumps [urllib3](https://github.com/urllib3/urllib3) from 1.26.3 to 1.26.4.
- [Release notes](https://github.com/urllib3/urllib3/releases)
- [Changelog](https://github.com/urllib3/urllib3/blob/main/CHANGES.rst)
- [Commits](urllib3/urllib3@1.26.3...1.26.4)

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